TABLE OF

CONTENTS

LIST

OF

ILLUSTRATIONS

SECTION ONE--INTRODUCTION

Main

Conponents

Case design

Differences from

520l1040ST

SECTION TWO..THEORY OF

OPERATION

Overview

Main

Systen

Microprocessing unit

GIue

Main

Menory

Direct l4enory

Access

MFP

Interrupt

Control

Audio/Video subsystem

Video

Video

Shifter

Display

Menory

GIue

Memory

Sound

Video

Control-Ler

Synthesizer

Interface

Input/output subsystens

MIDI

Intelligent

Keyboard

Parallel

Interface

RS232

Interface

Disk Drive Interface

Hard

Disk Interface

Systen

Startup

System

Errors

Functional block diagran

Systen clock diagra-m

11 t.2

t.2

I.5

2.8

2.8

2.9

2.70

2.Lt

2.L2

2.L3

2.t4

2.5

2.5

2.5

2.6

2.6

2.6

2.6

2.15

2.L6

2.t7

2.t

2.2

2.2

2.2

2.3

2.3

2.4

Mega

Service

Manua1 i.1

Table of

Contents

SECTION THREE--TESTING THE MBGA

Overview

Test equipnent

Test

Configuration

Trouble-Shooting a dead unit

ST

Diagnostic Cartridge

Power-up

RAM test

ROM test

Color test

Keyboard

MIDI test test

RS232 test

Audio test

Tining test

DMA test

Floppy

Disk test

Printer/Joystick test

High

Res

Monitor

Blitter test

Clock test

Expansion port test

Error

Codes

Quick Reference

SECTION FOUR--DISASSBMBLY/ASSEMBLY

SECTION FIVE-.SYMPTOM

CHECKLIST

Display problems

Disk Drive

Problens

Keyboard problens

MIDI problems

R5232 problens

Printer

Problems

Hard

Disk

Problens

Real Time Clock Problens

Blitter

Problens

3.

11

3.r7

3.r2

3.

13

3.t5

3.16

3.L6

3.L7

3.r7

3.4

3.4

3.6

3.7

3.7

3.9

3.9

3.

10

3.18

3.1

3.1

3.2

3.2

5.t

5.L

5.2

5.2

5.2

5.2

5.2

5.2

5.2

Mega

Service

Manual

í.2

Table of

Contents

SECTION

SIX.-DIAGNOSTIC

FLOIlICHARTS

SECTION SEVEN..PARTS

LIST

AND ASSEMBLY DRAWINGS

SECTION EIGHT-.SCHEMATICS AND

SILKSCREEI'I

SECTION

NINE--GLOSSARY

Mega

Service

Manual i.3

Tab1e of

Contents

LIST

OF

ILLUSTRATIONS

FIG

1

MEGA

COMPUTER

FIG

2

BATTERY

COMPARTMEI.IT

FIG

3

BACK

PANEL

FIG

4

I,EM

SIDE

PANEL

FIG

5

TOP OF

KEYBOARD

FIG

6

BOTTOM

OF

KEYBOARD

FIG

7

MEGA

MOUSE

FrG

I t{oNrron poRr

FIG

9

MIDI

PORTS

FrG 10

MoUSE/JOY

PoRTS

FIG 11

PRINTER

PORT

FrG 12

RS232

PoRT

FIG 13

EXTERNAL

FLOPPY

PORT

FIG 14

EXTERNAL HARD

DISK

PORT

FrG 15

FLJNCTTONAL

BLoCK

DTAGRAM

FIG 16

SYSTEM

CLOCKS

1.1

L.2

1.3

r.3

1.4

1.4

1.5

2.7

2.8

2.9

2.LO

2.tL

2.L2

2.L3

2.16

2.r7

Mega

Service

Manual

11

List of Illustrations

SECTION

ONE

INTRODUCTION

The

Mega

2 and

Mega

4 are

Motorola

MC68000 nicroprocessor based conputers with are styled as a nain

CPU

2 negabytes and

Mega sinilar

4 have a architectures unit with a to the detached

520ST/

1040ST keyboard.

The line.

Mega

They

2 has of

RAM, the

Mega

4 contains 4 negabytes.

Both the

Viega

2 built-in

1

Megabyte (720K fornatted) 3,5 inch floppy disk drive, and an internal switching power supply with built-in cooling fan.

size

Since of its the onty

RAM, difference this refers to both products.

nar¡ual between will use ' the

Mega

Mega

' as

2 and

Mega a generic

4 tern is the which

Power Light

Disk Drive

Drive Busy Light

Mega

Service

Manua1

ItIEGA

FIG.

1

COMPUTER SYSTEM

1.1

Introduction

The main components of the

Mega

2 and

Mega

4 are: o o o o o

CPU

Main board assembly

Disk drive

Power supply &

RF cooling fan

Shield

(upper and lower)

CPU

Plastic case

(upper and lower) o o o

KEYBOARD

Keyboard assembly

Interface board assembly

Keyboard

Plastics

(upper and lower)

MOUSE o o

Mouse board assembly

Mouse

Plastics

(upper and lower)

CASE DESIGN the

Figures keyboard

1 thru portion,

4 shows and the

CPU figure 7 portion shows the of the

IUEGA,

5 ar¡d

6 mouse.

shows

Battery Housing

Cover

--

size AA

Batteries

+

Top of

Computer

(-)

(+)

Mega

Service

Manual

FIG.

2

BATTERY

COMPARTMENT r.2

Introduction

On/Off lo

Power

Js

Printer

Midi ln

Frc.

3

BACK

PANEL loppy

I

Cartridge

Keyboard

FIG.

4

LEFT

SIDE

PANEL

Mega

Service

Manual

1.3

Introduction

Function

Keys

Calculator

Keypad

Arrow

Keys

FIG.

5

TOP OF

KEYBOARD

Bottom of

Keyboard

I

¡oyst¡Jx Port

I

Computer

Jack

V

I

MouseiJoystick

Mega

Service

Manual

FIG.

5

BOTTOM

OF

KEYBOARD

1

.ll

Introduction

Clicking

Left

Mouse

Button

Right Mouse

Button

FrG.

7

MEGA

UOUSE

Differences fron

520ST/1040ST o

New version of

T0S o

More nenory requiring

74LS243 buffers on

MAD lines o

ReaI tine clock chip

& support circuit, o

Graphics Co-Processor

(BITtsLiT) o Internal expansion connector & support circuit o

Cooling fan o

New case styling with detached keyboard

Mega

Service

Manual r.5

Introducti.on

SECTION T!{O

THEORY

OF

OPERATION

OVERVIEW

LSI

The

Mega

2 and

Mega

4 share a coruDon architecture, using the sa.ne

chip one ba¡rk set, and case styling.

Ttre only difference is the addition of of

2

Mega-bytes of

RAM, for a total of

4

Mega-bytes of

RAM on the

Mega

4.

Ttre hardware can be considered as consisting of a nain systen (central processing unit ar¡d support chips) a¡rd several

Input/Output subsystens

.

Main

System o

Mc680o0 running at

SMltz o

192

Kbyte

Read

Only

Memory o 2 or

4

Mega-byte

Randon

Access

Menory o

Direct

Menory

Access support o

Systen tining and Bus control o Interrupt control

Audio/Video

Subsystem o Bit

Mapped video display, using l2k bytes of

RAM, relocatable anywhere in nenory.

There are three display nodes available: a.

32O x

200 pixel,

16 color palette

îron jL2 selectÍons b.

640 x

200 pixel,

4 color palette fron !12 selections c.

640 x

400 pixet, nonochrone o

BITBLiT support o

Monitor interface analog:

RGB,

Monochrone o

Audio output: programmable sound chip with

J voices

Input/Output

Subsystens o Intelligent

Keyboard with 2 button mouse/ioystick interface o Parallel printer interface (Centronics) o

RS-232C serial interface o

DMA

Port

& connector for external drive o

Hard disk drive interface

&

Laser

Printer o

Musical instrunent network connunication

:

Musical

Instrunent

Digital Interface

(MIDI).

o

ReaI Time

Clock with battery backup o

ROM

Port

Mega

Service

ManuaL

2.7

Theory of

Operation

MAIN

SYSTEM

The main system includes the microprocessing unit, main nemory

(ROM and

RAM)

, general purpose DMA systen control, controller.

intepupt control, and

MicroProcessing

Unit data

The

Mega bus,

Z4 uses the Motorola

MC68000

16 bit external/32 bj-t internal

Uit address bus nicroprocessor, running at I

Mflz.

Glue

Glue (naned because it holds the systen together) is such an important component that it is involved in nearly every operation in thè computer. The functions nay be sumnarÍzed as follows:

KHz

Clock dividers-- takes ttre

I

Mtlz clock and outputs

2

Mllz and

500 clocks.

use¿

Video to tining--

B-Lank,

DE

(Display Enable),

Jlsync: gnd Hsync are generãtlsignals for the video display. operation (done by the

Operating

System).

There is a

Ìead/Write register in

Gtue wfrich nay be written to configUre for 50 or

60

Hz

Interrupt priority-- interrupts fron the

MFP and video tining are codeffisofpriorityonoutputsIP11andÍPL2tothe

68000.

These leve1s correspond interrupt,

HSYNC interruPt.

to no interrupts,

MFP interrupts,

VSYNC crrip

MFP,

Signa] and Bus qlbitration--

Glue decodes addresses to generate

Genàrator,

Memory devices from

Controller,

,

DMA

Controller,

Progranmable

Sound and ROMs.

DMA, Menory Controller,

It receives signals to synchronize data interfering with each other

(see

DMA below)

' from the transfer.

It arbitrates the bus during

DMA transfers to prevent

CPU and

DMA

IlleEal condition detectiq4--Glue asserts

Bus certain conditions are sized data to a word violated, sized such register, as or

writing to writing to

Error

ROM,

(BERR) writing system DeII¡ory

if

byte when the processor respond is in user mode.

AIso occurs if a device does not within the required tine linit.

For example, the

CPU tries to read from nemory and the

Memory

Controller does not assert

DTACK.

Mega

Service

Ma¡rual

2.2

Theory of

Operation

Main

Menory two

Main menory consists of

L92 kbytes of

ROM and one or banks

(2

Mega-byte each) of d¡manic

RAM. rn addition, the cartridge sLot alrows access to

128

Kbytes of

ROM.

All nenory is directly addressable.

The components of the ne¡nory systen are:

ROM, RAM,

RAM buffers,

Menory controller, a¡¡d

Glue.

Tt¡e

Operating System resides nostly in

ROM, wíth optional segnents loaded fron disk into

RAM.

R.{M is organized as

16 bit words and nay be accessed 16 bits at a tine or

8 bits at a tine.

Even nunbered addresses refer to the high I bits of a word and odd addresses refer to the low

I bits.

RAIII

ís made up of

1

Megabit

Mbytes, while giving two

X in tines

1 chips; the the

Mega in nemory, the or

4

Mega

4 there is

2 a¡r

Mbytes.

there are additional

16 chips, giving bank of L6 chips, z

BAM menory nap:

000008-000800

Systen nenory

(priveliged access)

000800-1FFFFF low bank

200000-3FFFFF high bank (Mega

4 only)

Note: the first

8 bytes of

ROM are napped into addresses

O-7.

These are reset vectors which the

68000 uses on start-up.

The

Operating Systen is located in two lMeg x I

ROM chips in current versions (192k).

Menory

Controller--takes addresses fron the address bus and converts to

Row

Address

Strobe

(RAS) and

Column

Address

Strobe

(CAS).

All

RAIì| accesses are controlled by this Atari proprietary chip, which is progrannable for up to

4

Megabytes of nenory.

Tt¡e

Operating

System determines how nuch

Eernory

Controller at poner-up.

Ttre

Memory

Controller refreshes the dynanic

RAMs, loads data during the

Video is present and prograns the

Menory

Shifter with display data, and gives or receives direct nernory access

(DMA).

Glue--decodes addresses for

RAM a¡rd

ROM a¡rd asserts output signals to enable these devices

(also decodes addresses for nost hardware registers to provide chip selects, functions.

See

Glue description above.

).

as well as nany other

Direct

Menory

Access

Direct menory access is provided to support both low speed

(25O to

500 Kilobits/sec) and high speed

(up to 8

Megabits/sec)

Sbit device controllers. The floppy disks transfer data via low speed

DMA and the hard disk (or other devices on the hard disk port) transfer at high speed. address

For

DlvlA to take place,

Controller many bytes) and the peripheral the Menory

Controller is given the of where to tal<e data fron or put data in

RAM, the

DMA is set up

(which channel, high speed or low speed, and how is given a comnand to send or receive data. The entire block of data (the size must be given to the

DMA

Controller and the peripheral before the operation starts) is then transferred to or from menory without intervention by the

CPU.

Mega

Service

Manual

2.3

Theory of

Operation

For ready exanple, in the floppy by fron a transfer conúro1ler previously. thè floppy

The

DMA controller,

Controller and the will process then wítl

Itr" äpecified number

ôr uyt"s has been transferred' nenory requesting data on

FDRQ.

will asserti"á ponO, tn" of

óue a sector signal the chip

DItlA, will

Controller

Ci".l

Glüe will signal the

Menory

Controller, fron read will read the byte fron the

DMA

Óontrotler a¡rd which was set up next byte the floppy the byte to nenory' that a byte is ar¡d signal the

Menory

Controller it in the address wait for repeat the until

Tra¡rsfers from to fJ-oppy are sinilár.

The floppy initiates every transfer by

This

At high speed

(hard disk is ready to transfer to or fron the

DMA chip, the

DMA assert

ACK reaa.

The

DMA

Controller can port), there is a difference: as a byte store up to l2 bytes

Controller will to tel tne peripheral know the byte

ís avaÍlable or has been is ,r."."".ry if the to transfer to ä.roty.

68000 is

Data nay using be the input lost or slowing down the tra¡¡sfer speed' bus, fron the in internal

De¡rory' and the

DMA nust port without wait being

MFP

InterruPt

Control are

ñ;

MFp

The

68901

MFP handles used.

MFp.

Each

Th;8 receives an interrupt up to

16 interrupts.

Currently all but one can be nasked inputs äre also directly inlerrupt input, or off or disabled readable generates an by by the progrernning

CPU. interrupt internally, if the interrupt is enatled,-MFPlyf witt be driven low.

When

When the ready to respond, it signals interrupt acknowledge the

CPU

Iow) and GIue

*nilI ."""tt r¡cr (interrupt acknowledge).

The MFP is

(Fco-2ìigh and vltlA will assert

DTACK and put a vector number on the data bus, which the cPU will read and use lo calculate the address of the interrupt routine'

The interrupts controlted by the

MFP are: nonochrone derecr

(MONOMOÑI-,--R5232

(including CTS,

999, RI), disk monitor

(FDINT a¡rd

HDINT), parallef'óort iine),'S'giO

IRQs gÚSV, display enable

(DE, equals start of ior keyboard and MIDI data, and

MFP timers.

display

MFp

ñoi árr l/O operations use interrupts.

The

CPU can also while waitini for an operation to conplete. The

MFP poll the has four timers,

RS232 used by tñe Operating

System for port for transnit and receive clocks' event tining and used by the

Mega

Service ltlanual

2.4

Theory of

OPeration

AUDIO/VIDEO

SUBSYSTEM

The

Menory video subsysten graphics processing consists video of the video display nenory, the controller,

Glue, a graphics control chip (video shifter), a output. The

Generator unit

(BImLiT)

, and a discrete section to drive the audio chip with a subsysten consists of a transistor output anplifier.

Progra.mnable

Sound

Video

Shifter

There are

16 color palette registers nay be used only one in row resorution,

4 is used in high resorution (actuarly, onry bit

0 of register

0 is used for inverse/nornal video).

Each palette is progr¡mmed for

8

Ievels

112 colors possible.

For a given

Ín the shifter. AII 16 are nay be used in high resolution, a¡¡d of intensity of red, blue, and green, so there are 8 x I x I pixel, the coror which is displayed is

= taken fron the palette referred to by getting infornation from each logical plane (see description of video dispray menory betow).

The shifter will output the red, green, and blue levers specified by that palette; note there are three outputs for each color.

Each output is either on or off. Thus, the nu¡nber of possible output levels is

Z to the lrd power

=

$.

The three outputs are sr¡nmed through a resistor network to monochrome proportion the voltage node, the color separate output.

level to give I equal steps. palettes are bypassed a¡rd there is

In a

Video

Display

Menory

Display nemory is part of nain nenory with the physical screen origin located at the top left corner of the screen.

Display

Eenory is configured as

1, 2, or 4 (nigh, nediun, or

1ow resolution) Iogical planes interwoven by

16 bit words into contiguous nemory to forn one 32

Kilobyte physical plane starting at a 256 byte half page boundary. The starting address of display

Eer¡ory is placed in the

Menory

Controller's

Video Base Address register by the

Operating

Systen or application. The

Menory

Controller will load display infornation into the video

Shifter

16 uits at a tine, and the

Video

Shifter wirl decode this infornation to generate a seriar dispray strean. rn nonochrone mode, each bit represents 1 pixer on or off. rn color, bits are conbined fron each plane to generate the comect level of red, green, and blue.

For the

Video exanple,

Video nunber nunber in low resolution (4 ptanes)

4 words are loaded into

Shifter for each word

(16 pixels displayed on the screen.

Tt¡e

Shifter conbines bit 0 from each word to forn a four bit

(0-15), and takes the color from the palette referenced by that

(e.s.

0101=5, use color from palette register !) a¡rd outputs those revers, then takes bit

1 fron each plane and outputs the coror from the palette referenced by those four bits, etc.

Mega

Service

ManuaÌ

2.5

Theory of

Operation

G1ue

GIue provides tining control to the Menory

Controller, video output, and monitor/RF output.

VSYNC input to the Menory

Controller causes the starting address the address counter during of the display nenory to be reloaded into vertical blanking.

DISPLAY EI{ABLE

(DE) tells the

Memory

Controller a¡¡d

Video

ShÍfter that a display line ís being scanned anâ data shoutd be loaded into the

Vídeo

Shifter.

BLANK shuts off the video output fron the

Video

Shifter during periods when the scan is not in a dilplayable part of the screen.

VSYNC and HSYNC both go to the monitor output a¡rd RF modulator.

These signals synchronize the nonitor or T.V. vertical a¡rd horizontal sweep to the display sigPal.

Menory

Controller

In addition to the inputs from

Glue nentioned above, there are two output control signals associated with video.

DCYC strobes data from display nenory lñto tne

Video

Shifter.

CMPCS active-only when changing the color

(color nap select) is attributes in the color palettes.

Sound

SYnthesizer

The yM2149

Progranmable

Sound

Generator

(PSG) produces nusic synthesis, sound effects, and audio feedback

The clock input

(e.g. alarns a¡rd key

ís 2 MHz; the frequency response range is

30

"ii"t "¡. tZJ

KHz,

There are three sound channels output fron the chip, which are míxed and sent to the nonitor speaker.

The pSG is also used in the system for various f/O functions relating to printer port, disk drive, and

RS232.

Atari Blitter

This

Iocation a

DMA device that moves block of nenory a destination location through a data fron a source given logic operation.

Single or multiple word increments and decrenents are provided for transfer r.s

to to destination. associated with the

There merging of are 16 possible source a¡rd logic operation rules destination data. In addition, with the

16 wõrd patterns ran a¡rd three L6 bit end-nask registers, the blit can also be used to perforn operations such as area seãd filling, pattern transformations, etc.

filling, brush line drawing, text and graphic

For more included infornation, please refer to the user nanual which is in the

Developer

Kit.

Mega

Service

Manual

2.6

Theory of

Operation

Real Tine

Clock with Battery

Backup

Ttris device has counters for

Time and

Calendar buÍIt-in.

Clock data are expressed with

BCD code.

The lower four address and data

Iines are used to program the device and access the clock through signal

RESET lines

RTCCS, RTCRD,

RTCh¡R which generated fron a decoder.

A line is also provided to reset the chip when the system is reset.

The naín clock supplied will be adjusted by a trimmer condenser so that it will output through the

CLKOIJII

JV battery down.

line a backup to the devÍce is a

32.768 l<hz oscillator which standard ca¡¡ be clock used signal to keep of

16.384 the clock

Xfrz. In addition, running during a power

For nore detail, nanufacturer

(RICOH please refer to part number

RP5C15) the application na¡rual fron the

Mega

Service

Manual

2.7

Theory of

Operation

Video

Interface

The

RGB a¡rd th¡o the

MONOMQN types input of interface nonochrone. The presence

(when

â

Iow).

The possible disPlays are: are provided of a nonochrone nonitor in nonochrone is the

Megas nonitor

ís connected, are a¡alog detected it will by be

Monochrome: single enitter foltower a.nplifier driving the output of the

Video

Shifter.

RGB: resistor network sums

colors

each have an output.

outputs emitter

for

each

color.

Ttre three

follower a.mplifier to

drive

Monitor Inputs:

Hsync--TTL

Vsync--TIL

Monochrone--digital

1.0V

R,G,B--analog 0-1.OV

Audio--1V. level,

Ievel,

P-P, negative, 3.3 negative, 3.3

1k

P-P' ohn.

P-P'

75

J! ohn.

k k ohn.

ohn.

ohn.

û

Monitor

1

-

2

-

3

4

-

-

Audio

Out

ComPosite

SYnc

General PurPose OutPut

Monochrome Detedt

5

6

-

7-Red

I

9

-

-

-

Audio ln

Green

Plus 12-Voll Pullup

Horizontal SYnc

10

11

12

13

-

-

-

-

Blue

Monochrome

Vertical

Sync

Ground

FIG.

8

MONITOR

PORT

Mega

Service

Manual

2.8

Theory of

Operation

rNPUT/oUTPUT

SUBSYSTEMS

Musical Instrument Connunication

The Musical Instrunent Digital Interface (MIDI) allows integration of the

Mega with ilfornation is nusiõ provided sysnthesizers' by two sequencers' boxes

HiSh speed

(3L'25

Kilobaud) as¡rnchronous current loop serial communication ptog"an

"rrd oUT also supports the optionat thar data by one stoP and other devices fossessing

MIDI interfaces. co.rsi"f'ãi bit.

8

A.t. bits preceded ports, ttlt¡t ntnu by one

MIDI port) gUT of

. MIDI start bit the keyboard and MIDI

IN specifies a¡rd followed writeJ-to

6850

Connunication to l[ã-OóiO the transistor

MFP chip interrupt controller. outside via trdo on takes in the input through two inverters

THRU place response inverters on to via interrupts the side. a

6850

Ttre

The nCfe. The which systen is tra¡rsnit side are input signal

CPU passed interfaced a¡rd to the output connector where reads fron in order to allow chaining of nultiple devices on the

MIDI bus' and the to the an

LED/photois routed around it is called

II{IDI

Js

J¡

Midi

Out

1

2

3

4

-

-

-

-

5

-

THRU

Transmit Data

Shield Ground

THRU LooP Return

OUT

Transmit

Data

OUT LooP Return

Midi ln

1

2

3

4

5

-

-

-

-

-

Not

Connected

Not

Connected

Not

Connected lN

Receive

Data lN

LooP Return

FIG.

9

MIDI

PORTS

2.9

Mega

Service

Manual

Theory of

OPer'ttion

Intelligent

Keyboard

The keyboard trarismits nake/break key scan codes, ASCII codes, nouse of-day data, joystick data, in data requests

(year, month, day, hour, minute, second) in response to device a¡rd on the keyboard assenbly by the lMHz

8 bit

HD6301

Unit.

The

HD6301 has internal

RAM and

RoM.

Included in

ROM whenever the

RESET connand by the

CPU.

The

MC6850 interrupts which are passed response by the

CPU.

Comnunication

6850

Microconputer are self-test diagnostics is is read to is controlled on the nain board by a which a¡¡d the

CPU to are sent over by external perforned the written to

Èhe serial by the

MFP events, at

CPU and tinepoh'er-up connunication in interrupt and line response to controller.

The

2 Button

Mouse is a¡r characteristics: a resolution opto-mechanical device with the following of

100 counts/inch, a mæ<imun velocity of

10 inches/second and a naxinum pulse phase error of

50 percent.

The joystick/nouse

Ieft button.

The right button equals the joystick trigger, a.nd the left button four is port has inputs for up, down, left, ríght, right button, wired directions to the

(up, second down, joystick port trigger. etc. ) and one trigger.

The joystick has v

Mouse/Joystick

1

-

2

3

4

5

-

-

-

-

Up/XB

Down/XA

Left/YA

Right/YB

Not Connected

6

-

Fire/Left

Bulton

+sVDC

I

9

-

-

Ground

Joyl

Fire/Right Bulton

Joystick

1-up

2

-

Down

3

4

5

6

-

-

-

-

Lefl

Right

Reserved

Fire Button

7-

+SVDC

8

9

-

-

Ground

Not Connected

FIG.

10

MOusE/JoY

PoRT

3

2.ro

Theory of

Operation

Mega

Service

Manual

Parallel

Interface

The parallel port is prinarily intended as a Centronics type printer interface, but can also be used as a general purpose r/0 port.

centronics

STROBE and

BUSY are supported.

BUSY is read by the

MFp chip.

Data and strobe signals are output by the

YM2149 psc chíp. Not all

Centronics on the ohn data printers lines are should resistor pull-up on compatible not the exceed printer with this port.

2.3 mA. side.

)

(TtrÍs

The current corresponds to loading a

2.2k

Ttre port can be programned to be read directly by the

CPU, with

Gtue chip select.

input or output. doing address

The decode

PSG to chip is provide

ç

Printer

1

-

STROBE Output

2-Dala0

3-Data1

4-Dala2

5-Data3

6-Data4

7-Data5

8-Dala6

9-Dala7

FIG.

11

PRINTER

PORT aaaaaaaaaaaaa aaaaaaaaaaaa

?5 .r¡ 2l :2 l! 2f 19 16 rr 16

!5

10

11

-

-

12-17

Not Connected

BUSY lnput

18-25

-

-

Not

Connected

Ground

Mega

Service

Manual

2.17

Theory of

Operation

RS232C

Interface

The

RS232C interface provides asynchronous serial connt¡¡¡ication with five handshake control signals:

Reguest to

Send a¡rd

Data

Terninal

Ready are output by the

PSG chip;

Clear to Send,

Data

Carrier

Detect, and

Ring

Detect are input to the

MFP chip.

The

MFP contains a

USART

(Universal

Synchronous/Asynchronous

Receiver/Tra¡rsnitter) which handles data transmission and reception.

The 2.4576

MHz clock to the

MFP is divided by the clock for second tiner receiver

D and

(pin are supported. f488

16) output transnitter. of

Data tine drivers the and

MFP rate of

1489 to

50 provide to

19200 the bits line receivers basic per with

+/- I2v. supply meet the

EIA

RS232C standard for electrical interface.

\

Modem

1

-

2

-

3

-

4

-

5

6

7

8

-

-

-

-

9-19

Protective Ground

Transmitted

Data

Received Data

Requesl to Send

Clear

Not Connected

Signal Ground

Data Carrier RePeat

- lo

Send

Not Connected

FIG.

T2

RS232

PoRT aaaaaaaaaaaaa aaaaaaaaaaaa

2t

'¡

20

21

-

-

22

-

23-25

Data Terminal Ready

Not Connected

Ring lndicator

-

Not Connected

Mega

Service

Manuaf

2.L2

Theory of

Operation

Disk Drive Interface

The

Mega conputers have a built-in floppy disk controller

(a lrJestern

Digital double sided

L772) and logic for selecting up to trr¡o single or drives.

The

Mega has one built-in floppy disk drive a¡rd provision for one external disk drive. The hlestern

Digital

WDt772

Controller services both drives.

Drive and side selection is done by outputs on the

YM2149 PSG chip.

The

CPU reads a¡rd writes to the

L772 through the

DMA

Controller,

Tl:e

1772

Ínterrupts the

CPU on the

INTR

Iine, via the

MFP interrupt controller.

Tl:re

L772 accepts high level comnands, such as seek, fornat track, write sector, read sector, etc.

and passes data to the

DMA

Controller (see

DMA controller under

Main

Systen, above, for details on

DMA tra¡rsfer).

The L772

ínbemupts the

CPU when overhead the operation of disk

I/0.

is conplete.

The

CPU is freed fron nuch of the

Mega

Service

Manual

I

Floppy tlsk

1

-

Read Dala

3

-

4

-

Logic Ground lndex Pulse

6-DrivelSelect

7

I

-

-

9

10

-

-

Logic Ground

Motor

On

Direction ln

Step

FrG.

L3

EXTERNAL FLOPPY PORT

11

12

13

14

-

-

-

-

Write

Data

Write Gale

Track 00

Write Protecl

Theory of

Operation

2.13

DMA

Port;

Hard

Disk Interface

The hard disk drive interface is provided through the

DMA controller; the hard disk controller is off-board and is board a¡rd is sent conna¡¡ds via an

SCSI-like

(SnaII Conputer

System

Interface) command paraneter block.

Data is transferred via

DMA.

l,Jriting to the externâI controller causes

HDCS

(Hard Disk

Chip

Se]ect) to go low and

CAl to go high.

DMA tra¡¡sfers are controlled by the external device. fJhen data is available, or the device is ready to accept data,

DMA acknowledge

Memory

HDRQ will be driven high by the external

Controller.

Transfers can take place controller.

The chip nust respond within 2!0 nanoseconds with ACK

(}ow) to that data is on the bus or has been read fron the bus-

The

Cóntroller feeds data to or accepts data fron the

DMA at up to

1

Mbyte/second.

a

Had

Disk

1-Data0

2-Dala1

3-Data2

4-Data3

5-Data4

6-Data5

7-Data6

8-Data7

9 Chip Select

10

11

1

2

-

-

-

- lnterruPt Request

Ground

Reset

FIG.

14

EXTERNAL HARD

DISK

PORT aaaaaaaaaa aaaaaaaaa

13

14

'15

16

17

18

19

-

-

-

-

-

-

-

Ground

Acknowledge

Ground

A1

Ground

Read/Write

Data Request

Theory of

Operation

Mega

Service

Manual

2.r4

SYSTEM

STARTUP

After a

RESET

(power-up

or

reset button)

the

68000

will

start executÍng

(GIue maps

000004

at

8 bytes points

FEFFFF). the address pointed

The following sequence to by locations

4-J,

which

is

RoM

of

ROM

at

FC0000-J

into

the addresses

0-7).

Location

to

the

start of

the operating systen code

in

ROM

(FCOOOO-

is

then executed:

1.

Perforn a reset instruction

(outputs a reset pulse).

2.

Read the longword at cartridge address F40000.

If the data read is a

"nagic nunber", execute fron the cartridge

(diagnostic cartridge tal<es over here).

If not, continue.

3. Check for a warn start

(see if

RAM locations vrere previ.ously

written), initialÍze the nenory controller, and continue running the application which was running before the reset if it was a warm start.

4.

5.

6.

Initialize the

PSG chip, deselect disk drives.

Initialize color palettes a¡rd set screen address.

If not a h,arn start, zero

De[¡ory.

7.

Set up operating system variables in

RAM.

8.

Set up exception vectors.

9.

Initialize

MFP.

10.

Set screen resolutÍon.

11.

Attempt progran to boot floppy; attenpt to boot hard disk; run if succeeded.

SYSTEM

ERRORS

The 68000 place when an when has a feature calted exception instrtrctions are executed.

An exception processing, which takes

Ínterrupt or bus error is indicated by external logic, or the

CPU detects an emor internally, or when certain types of wiII cause the

CPU to fetch a vector (address to a routine) fron

RAM and start processing at the routine pointed to by the vector.

E:<ception vectors are initialized by the operating system.

Those exceptions whích do not have legitimate occurrences (interrupts being legitimate) have vectors general purpose routine which on the screen (nushroon clouds in older versions of disk loaded operating systen). The number of bonbs equals the nunber of the exception which occurred.

pointing to a wiII display some nunber of bonbs showing

Mega

Service

ManuaL

2.15

Theory of

Operation

System errors nay or

¡nay files from disk wiII cause the

Verify the diskette and disk computer.

not be recoverable. system to crash,

Errors in drive before attempting loading necessitating a reset.

to repair the

NUMBER

(No.

OF

BOMBS

AND

MEANINGS

26,28,30, ana 64-79 wiII not bomb, as they are legitinate.

)

5

6

2

Bus

Error.

Glue asserted bus error or

CPU detected an error.

] Address

Error.

Processor attenpted to access word or long word sized data on an odd address.

IIIegaI Instruction.

Processor fetched an instruction from

ROM or

RAM which nas not a legal instruction.

Zero

Divide.

Processor was asked to perforn a division by zeto.

Instruction.

This is a legal instruction, if software uses

7

B

9

Chk this, it nust install a handler.

Trapv

Instruction.

Privilege location

Trace. execute

See Chk instruction.

Víolation.

CPU was in user mode, tried to access a in supervisor address space.

If trace bit is set in the status register, the

CPU will sofuware.

this exception after every instruction.

Used to debug

10

Line 1010 Ernulator.

CPU read pattern

1010 as an instruction.

Provided to allow user to emulate his own instructions.

11

Line

1111

Emu1ator.

See

Line

1010

Emulator.

12-23

Unassigned, shouLd be no occurrence.

24

Spurious

Interrupt.

Bus error during interrupt processing.

25-3L Autovector

32-63

TRAP

Interrupt. ion processing.

Even should have no occurrence.

Instruction.

The

CPU nunbered read vectors are instruction which used, forced others except-

64-lg

MFP interrupts.

BO-255

User interrupts.

Note: If you have an emor nessage such as

"T0S

ERROR

35", then the possible errors are:

1-

The file in progress is bad.

2-

The total number of folders in the sysLem has exceeded the

4O-folder can be used to linit.

However, there is a program which extend this limitation

3-

No ha¡rdles left or too nany open files.

on folders.

Mega

Service

Manual

2.L6

Theory of

Operation

=

æ p)

Ø o ts.

o o

Þ

P v

Ê o

ìt o

H) o

ì5 o

õ

Þ cl

P.

o r20vAc c)

7

=

41 z c)

Ê

H z tr.

,71 o.

F-r t.c)

C) i(P tt

H

\tl

CONTROL

BUS t(

MoNo

RGB

*

VIDEO

DISPLAY

32MHZ

+lzvDc(1 6

A)

+ sVDC(3 0

A)

JOYSTICK

MOUSE

OUT

MIDI

DMA

IN

THRU

I

KEYBOAFD

DRAM CONTROL niEMORY

CONTBOLLER t^IT

MEMOFY

DATA

BUS

MEGA

FUNCTlONAL

BLOCK

DIAGRAM

2t88

R5232

PORT

VIDEO/AUDIO

CONNECTOF

I rk

TXD

MONO

MON

¡lf

VSYNC

*

HSYNC

* coPyRtGHT

@ 1988 ATARI CORPORAIION

o

H)

O

ìd o

4

ID a?

P, o a: o o

7t ts.

o o

)

=

ç

çD ts

3 o

æ

ID

Ø o

ÈJ

P

P

Õ

(t)

F]E rTJ

H

=G) c) oo\ x

Ø

KEYBOAÐ

XTAL

IN

VIDEO

SHIFTER

39 16Àitlz

5

MEMORY

CONTROL

UNIT t6

38¿t

KHZ

TPI vdd o t

Va"

32 768 KHZ

MEGA SYSTEM

CLOCKS

BL¡TÏER

LK

68ooo

CPU

21 49

PSG

1772

FDC

12v

!3v"" ccPlFEHr

@ ls

ATAR COFFOFA'IÛ\¡

SECÎION

THREE

TESTING

OVERVIEI{¡ cartridge should be used if possible. If the unit gives no display or

R5232 output when running the cartridge, see rrTroubleshooting a

Dead

Unit'r below.

Ttris section pertains to the test equipment, diagnostic software, and test procedures used to verify repair the

Mega/ST computers.

Tt¡e diagnostic correct operation and

Since the level of conplexity in the

Mega/ST systen is high, it shouldn't be expected that this docunent can cover all possible problens or pinpoint the causes; rather, the intent here is to give a systematic approach which a technician can use to narrolt down a problen to Íts nost likely source. troubleshooting conputer systems

68000 processor nay be consideration; due

Experience in is assumed. Knowledge of the helpful.

Economics witl be arì

ínportant to the low cost of the

Mega/ST conputer line, little tine can be justified in troubleshooting down to the component level when sub-assembly.

Many naybe of socketed, naking it the may

¡nore be cheaper to expensive (and verification and exchange critical) replacenent the cotrponents faster.

entire

TEST

EQUIPMEI.¡T

The following equipnent will computer: be needed to test the

Mega/ST

I

* t

ì t

I r Atari

SCl224

RGB

SM124

Monitor

Monochrone

(or sinilar)

Monitor

(or siniJ-ar)

SF354 or

SF314

Floppy

Disk

Drive

Mega/ST

Mega

Port

Expansion

Test

RS232

Loop-Back Connector

MIDI

Loop-Back Cable

Mega/ST

Test

Diagnostic

Diskettes

(2)

Test Fixture

Fixture

(Mega only)

Cartridge (Revision

4.0)

RS232 ternirral

(or

Mega in tff52 enulator node)

In addition, the following itens will be necessary to troubleshoot and repair failed computers: r

*

*

(100MHz Recconmended)

Multimeter,

1l

FS

(or better)

Snall

Ha¡rd

Tool,

&

Soldering lron

Spare Parts

Mega

Service

Manual

3.1

Testing

TEST

CONFIGI.JRATION

With the power

(IMPORTAI.IT--if switch off, Ínstall the Diagnostic the cartridge does not have the

Cartridge plastic enclosure,

BE

SURE

THE

CARTRIDGE

Connect cables

IS

INSTALLED

WITH

THE CHIPS FACINC DOIW)

.

fron test fixture into the hard disk port, parallel port, and joystick / nouse ports. The ioystick cables should be plugged cornputer in so that, if the fixture ports were directly facing the ports, the cables would not be crossed.

PIug the

R5232 and MIDI loopback connectors into their ports.

PIug the color nonitor into the nonitor output

(a nonochro¡ne can be used instead)

Power few seconds skip down on the to " the unit. nenu screen

Mega/ST

Some tests should

Diagnostic will be next section

"Troubleshooting a

Dead

Unitrr.

run appear. If

Cartridge

", autonatícally; the screen below.

If not, in appeArs, a read

If the unit is being used as a terninal for a host computer, it should be disconnected fron the host before using the diagnostic; otherwise, the host nay think soneone is logging oD, and will send diagnostic.

nessages which will act like keystrokes input to the

TROIJBLESHOOTING

A

DEAD

UNIÎ

In the event that the systen is correctly configured and pclwered a¡¡d determining no display appears, the problen.

This this is the procedure to use for assr¡nes elementary steps have been taken, such as checking the

LED in the forward left corner of the compu+,er to verify the unit is powered and naking sure the nonitor is working.

1.

Connect a dumb terninal to the

RS232 port of the unit under test

(IJ.U.T.

).

You can use an Mega/ST running the l/T52 terminal emulator program--see the owner's nanual for setting up tÆ52.

The cable should connect pin 2 (serial out) of the U.U.T to pi.n

3

(serial in) of the terminal, a¡rd vice versa.

Connect pin

7

(sround) to pin 7.

The terminal should be set up for

9600 bps, I bits of data, 1 stop bit, no parity (this is the default condition for the

VT)2 enulator).

Insert the

Diagnostic

Cartridge into the U.U.T.,

8¡¡d power on the unit. If the

Diagnostic

Cartridge messages appear on the display of the terninal, use the diagnostic to troubleshoot tire computer.

If not, the conputer will have to be disassenbled to iroubleshoot. Refer to

"Diagnostic Cartridge" below for information on using the cartrÍdge.

If no activity is seen on the

RS232 port or display, continue with

(2) next page.

Mega

Service

Manual 3.2

Testing

2.

Disassenble the conputer so that the printed circuiÈ board is exposed (see a¡¡

Replace

68000

CPU.

Section

4,

Disassenbly).

Power up the conputer.

Using oscilloscope, verify the

SMHz clock to the

68000

CPU

(pin

15).

oscillator if necessary.

Tt¡en check pin

17

(HALT) of the

It should be a TIL high. If so, go on ro I below.

If not, the

CPU is halted.

The reasons may be: (1) bad reset circuit,

(2) doubte bus error, 3) bad

CPU.

Check

(1) bV observing signal on input of the tn¡o inverters on the

HALT line.

Check

(2) by observing should pín conponent

22 of the

CPU (BERR) as the unÍt is powered on. It be high always. If there are logic low pulses, some is malfunctioning a¡¡d

Glue is generating the error.

Verify the clocks to

GIue a¡rd

Menory

Controller and replace these conponents to verify then

(if socketed).

If still failing, the

CPU is unable to read

ROM or there is a conponent wlr-leh is not responding to a read or write by the CPU, probably the

MFP

68901 or

DMA

Controller.

The

MFP should respond to an

MFPCS with

DTACK.

The

DMA chip should respond way to check

(3) other to than

FCS by by asserting RDY.

There is elinination of the other no two possÍbilities, although a hot

CPU

(too hot to touch for nore than a second) strongly indicates a bad

CPIJ.

3. If the

CPU is not halted, it should be reading instructions f'ron

ROM be

(cartridge, if installed) and data a¡¡d address lines will toggling. (If not, replace

CPU.

) At this point, there is the possibility that both the video and RS232 subsystems are failing.

Verify the output of the

MFP chip (pin 8) while powering on the unit with the cartridge installed. If data is being sent. trace it through

RS232. the

1488

If all connection to driver.

Note that

+ a¡rd

- 12v. is required for looks good, the terninai.

there nay be sonething wrong with the

Verify also the output of the

Video

Shifter. If using an

RGB nonitor, check the outputs to the sunnirrg resistors (if external) for

R,

G, a¡¡d

B.

Note that if

BLANK is not going high, no picture will be possible. If using nonochrone, check output pin 30.

AIso check does the not output on input to read a the low on

MFP, this the

Video

Shifter.

pin 29, signal

M0N0M0N.

Note on power-up, that if

Ít will the cause

CPU

RGB

If the

Video

Shifter is outputti.ng a signal, but the picture is unreadable, there is probably a problen with screen

RArY.

The cartridge should be used to terminal as a display device.

diagnose this problen, with the

RS232

Mega

Service

Manual 3.3

Testing

MEGA/ST DIAGNOSTIC

CARTRIDGE

The diagnostic cartridge is used to detect a¡rd isolate conponent several failures in the conputers

(52O/LO4O and Mega).

There are revisions; this docunent refers to revision 4.0.

Users of earlier versions should refer to the appropriate

Troubleshooting

Guide.

This section gives a brief guide to use with a description of each test, error codes or pass/fail criteria, and recommendations on repaír.

Power-up

The diagnostic program perforns several tests on power-up. In particular, the nessage

"Testing MFP,

GIue tining, Video will appear, a¡rd the screen will appear scrambled for a few seconds before the menu is printed.

The screen will turn red

(dark background in nonochrone) if a¡r emor occurs in the initial testing, with a message indicating the failure. The lowest

2

Kbytes of

RAIü is tested on power-up; if a locatíon fails, the error wiII be printed to the

R5232 device. It is assumed that if

RAM is failing, Lhe execution will fail screen nay because there not be is no readable a¡¡d stack or system program variables.

The progra¡n will continue to test

RAM and print emors, but no screen will be displayed

(the screen

¡nay turn red).

Repair

RAM.

If the keyboard fails, it will be inactivated.

The user nust connect a terninal to the

R5232 port.

The diagnostic progra¡n looks for keystrokes fron the

RS232 device.

If the display is unreadable, the

RS232 terminal should be used. All nessages are printed to the

R5232 port as weII as the screen.

Test

Menu

The normaL screen will be dark blue with white letters.

The test title and revision nunber are displayed at the top, with the anount menu nunber cause before sone of below that. To corresponding iterations of the test or tests chosen ca¡r be run by typing in the of

RAM tests and keyboard to those tests, and then the return key.

Many cycles the test before just completion, hit the controller select before sequence to the tests, the user types the typing run escape test stops). revision

RETURN. key (there

As each below,

Typing continuously. nay be and a test keys a zeto will

To stop a sone cycle delay cycle conpletes, in the total numbers of cycles will be displayed on the screen.

Mega

Service

Manual

3.4

Testing

MAIN

MENU

Mega and

4u nnu

ST

Field Service Diagnostic

o

1987,

Atari

CorPoration--

Keyboard revisioi-V----6O

Test Rev' 4'0

n"

0S

Version

2

USA

NTSO

G

L

X

R

K

A

F

0 z

RAI{

Test

0 0'S'

ROltls

Keyboard

M

MIDI

Audio

Fioppy

T

Timing

Oisk

P

Printer/JoY

Ports

Graphics chiP

ReaI-tine clock

(Blitter)

Expansion connector

Run

AII

Tests iun rnternal tests

(R,o'c'K'A'T'L'G)

E

B

V

?

Exanine/ModifY nenory

Set RS2l2 rate iãÀgr"

iia"o

outPut--5o/6o

Hz

Help

Enter letter(s), and

REIURN c

S

D

H

CoIor

Serial

Port

DMA

Port

High resolution ons will be highlighted if these e.

These should be

Present in tion requires the exPansÍon test quires disassemblY)

' If these ishted, the test wirl check for hrough seleðtion sequences through

RAM' tests. all the tests

Selection

'E' except for enables the or hardware registers' The 'B'

Pressing decreases the up it.

Pressing cartridge functions.

arrovJ

'?' or the

HELP key e baud rate on increases it' brings up a the

RS232 Port' pressing the brief down arrovr¡ synopsis of the

After a test or series of tests conpletes' the status arrA er"ãr-".po"t, if any, will be pass/fail displayed' Press the space bar to return to the nenu'

If nultiple tests are selected' before completion by pres"ins-ihã

BéC the current either test, continuini the or sequen"å returning

"iff will be

" "or,"id"iabte delay Uãfore

iup-lã

i the sequence tey. Át ttte conpletion of hali, with the options of nenu' In some cases there the current minutes with test conpletes and

4 can meg be halted

of

RAM'

)

Testing

Mega

Service

Manual

3.5

Sumnary of

Tests

RAM TEST

RAM is tested in three stages: low

2 kbytes, niddle (up to

64t¡, a¡rd fron 64t to top.

The test patterns used are: all ls, all

0s, a counting pattern

(data=low word of the address) counting counÈing pattern

(data=conplenent of address

' reverse

The pattern is copied fron the top and botton of a

J2 Kbyte buffer into the current

J2

Kbytes of video

RAM, then shifts video

RAM to a new area, verifies the pattern, and repeats the test, until the top of

RAM is reached.

Finally, addressing at

64t boundaries is checked by writÍng unique pattern in last 216 bytes of each

64t

Utoct.

If an error occurs, the error code is displayed, followed by the address, data agree.

E.g.: "

R2 written, data

45603E W:603E read, and

R:613c bad the bits: bits

1,8".

which did not

In units having nore than one ba¡rk

(i.e.,

1040ST,

MEGA4) the address correct as well chip.

The as the bit position following table the addresses and banks for various nust gives a models: be used to find correspondence the between

O-7ffff

Soooo-rrrrr

100000'lfffff

200000-3fffff

520 bank

0

1040 bank

0 bank

1

Vlega

2 bank

0 barrk

0 bank

0

Mega

4 bank

0 bank

0 bank

0 bank

1

(A bank is a

16 bit wide group of

RAMs.

A bank nay consist of

256k bit chips--256k x

16 =

4 UUit or

JL2k bytes--or lMbit chips--lMbit x

16

=

16

Mbit or 2

Mbytes.)

RAM ERROR

CODES

Except where corresponding noted, repair by replacing the

RAM chip to the indicated bit(s).

R0--1ow nenory failed while setting up to run test.

Rl--failed walking 1s or

0s.

R2--failed address (counting pattern)

.

RJ--failed

64t< boundary test. Probable failure in

Controller.

Memory n4--failed while displaying area tested (video

RAM).

Mega

Service

Manual

3.6

Testing

ROM TEST

(PAL

128K

Ttris test reads the configuration bytes of the operating systen or to deternine the version, tanguage/country, and TV standard

NTSC). and the checksuns are calculated.

These values are conpared against known value with checksuns for this version to deternine if there may be

AII good only

The checksun expected bytes or bad. two

ROMs

ROltls; sone have two 1 neg

ROM'S).

test fails if for from

Six the in operating checksuns the are displayed, machine (sone checksun system calculated the configuration byte

ROMs machines does are not then although have natch found (e.S. read six the

Version

2,

French).

Incorrect checksums are indicated by a nessage.

If an error is displayed, replace the correspondÍng ROM.

In a two

ROM set, replace the low

ROM if any of

L0, L1, or

L2 showed an error, or replace the high

ROM if any of H0,

H1, or

H2 showed an error.

New revisions incorporated receive

T0S into of

T0S witl the current cause version this test to fail if of the diagnostic. If revisions before receiving the diagnostic will be necessary to verify the checksr¡¡ns yourself.

not you revision, it

COLOR TEST

Each

This test verifies the

Video

Shifter.

Seven color ba¡rds are displayed: red, green, blue, cyan, nagenta, yellow, and white.

band are represented, each screen consists of 8 leve1s of intensity. All

16 color palettes palette is a vertical strip across the

(strips should not be discernable, but each color should be a straight líne across the screen).

Because of the tight tining involved, keystroke intemupts will cause the display to jitter.

The operator should see that there are no gaps or missing sca¡r outputs on lines in the display. If lines are nissing, check the three the

Video

Shifter for that color, and verify the values of the resistors on the output.

Too low a brightness setting on the nonitor will cause the nonitor not to distinguish between fine levels, making it appear there are only four levels being output.

The

Video sunmed

Shifter green (G0, G1, G2) and together by a has three outputs for blue (80, 81, resistor network to red give

(R0, R1, eight

R2),

B2l.

Each of these triples is levels of intensity for each color, depending on which of the outputs are on.

The values of the resistors give different weight to each output.

The value of the resistor at

R0 is twice that of R1, which is twice that of

R2.

This allows us to get

8 equal steps on the sumned outputs.

For exanple,

R0 on

Rl and

R2 on =

7

/8. this signal

,

R1 and

R2 off

=

L/8,

R0 off, then passes through a transistor anplifier, and fron there to the video nonitor connector.

NOTE

: this resistor network is incorporated into the full custon chip in later versions of the video shifter

(C101608).

Video shifter which has part nunber

C101608 or

CO7O7I3 has pin

1 connected to to signal line

BLANK.

Shifter with part nunber

CO259I4 will have pin

1 connected to a pull-down resistor

R144,10K, and signat line

BLANK will be connected to diodes D9,

D10,

D11.

Mega

Service

Manual

3.7

Testing

Symtons and fixes:

1.

Missing prinary color.

Check the output of the transistor anplifier.

06 is blue,

Q7 is green,

Q8 is red.

Look for a staircase pattern (eight levels of intensity). If the signal is there, trace forward to the video connector, if not, trace backward found.

to the

Video

Shifter, until the faulty conponent is

2. Prinary colors present, secondaries níssing or incorrect.

Replace the Video

Shifter.

3.

Coarse change in intensity

(not a snooth dark to light tra¡rsition).

Replace Video

Shifter or look for a short on the output color.

of one of the three color outputs for the appropriate

4.

Specks or lines on the screen.

This can be caused by bad

RAM; if

RAM has been tested a¡rd is good, replace the

Video

Shifter.

5.

Wavering display, horizontal lines not occurring in the sane place every tine.

The processor nay be getting extra interrupts (if the processor is required to handle additional interrupts, it will not have tÍner to change aII L6 color registers during a horizontal scan time).

Exanine the

MFP interrupt request

(pin

32).

There should be an interrupt every

L26 mícroseconds

(2

(pin the inputs display lines) fron

Display

Enable

20). If additional interrupts occur, locate the source: at pins

22-29 should all be high. If no external

(to tne

Ufp) source for the interrupts is found, replace the

MFP.

NOTE: if the keyboard is not connected, the input to the

6850 will be low, causing continual intemupts.

KEYBOARD TEST

Two types of test are run.

The keyboard self-test is done first, and if this passes, a screen is displayed representing t'he keyboard.

If multiple tests have been selected, only the self-test is run. The operator presses keys and observes that the comesponding character on the screen changes

(reverses background color). The key will also be displayed in the lower half of the screen. The mouse buttons a¡rd four directions are also shown on the screen.

Connect the mouse and nove in any direction a¡rd the arrow will flicker.

Any key clicks while the

¡nouse is noving indicates a short.

The self-test checks comnunication between the

CPU and the keyboard nicrocomputer, microcomputer, and scans and checks

RAM the keyboard for and

ROM stuck in the keys.

keyboard

Mega

Service

Mar¡ual 3.8

Testing

KEYBOARD ERROR

CODES

KO--stuck key.

A key closure was detected whire the keyboard self test was executing.

K1--Keyboard not responding. processor and no keyboard needs the

6850 is to status was returned be replaced not functional.

A or connand the nas sent to the keyboard within the allowed tine.

Ttre connunicatÍon channel through

K2--Keyboard status error. keyboard, on conpletion of status.

Replace the keyboard.

The the setf test test, coûDand the was keyboard sent sent to an the error

MIDI

TESTS

This test sends data out the

MIDI port, (data loops back through the

MFP the cable) a¡rd reads fron the input and is correct. This also tests the interrupt fron the

68J0 through chip. sent (not all

The

LED cables in have the the loopback

LED).

cable verifies the data will brink as data is

MIDI

ERROR

CODES

MO--Data not received.

Trace the signal from the output of the

6850, through the drivers, loopback cable, and receivers to the input of the

6850. Replace the defective component.

M1--ldrite/Read data nisnatch.

Ttre data b'ritten was not the same as the data read.

Replace

6850.

M2--Input frane noisy signal error. ga¿

6850 or bad driver or receiver causing

MJ--Input parity error. noisy signal.

ga¿

6850 or bad driver or receiver causing

M4--Input data overrun. The previous byte was read. the

MFP not responding

6850 received

Probable bad

6850, a byte before also to the interrupt request.

can be the caused by

Mega

Service

Manua1

3.9

Testing

RS232

TESTS t'irst the

RS232 control lines are tested

(which are tied together by the loopback connect,or), then the data loopback is tested. Data is checked transnissing?receiving using a polling nethod first, then using interrupts.

Data is transnitted at 300, 600,

LãOO...t92OO bps.

Data tra¡rsnission and receiver is perforned by the

MF? and the

1488 and f489 driver chips.

Interrupts are a function of the

MFP.

Control lines are output by the

PSG chip and input on the MFP.

Note that this test does not thoroughly test the drive capability of the port, as the

RS,232 device nay requÍre voltage swings of

12 volts

& there are no load resisters in the serial port diagnostic connector.

If the test passes, but the unit fails in use, it is likely that the

1488 or f489 cfrips are bad.

R5232

ERRoR

CoDES

Data transmission error:

S0--Data not received.

Check signal path:

MF? pin

8 to

J6 pin

2 via

1488 to

J6 pin

3 to

MFP pin

9 via

1489.

Sl--Daca nisnatch. Data read was not what was sent.

Check integrity of the signal.

May be bad driver, receiver, or

MFP.

S2--Input frane

Probable

MFP error. Incorrect tine between start and stop bits.

failure.

S3--Input parity emor.

Probable

MFP faÍIure.

Input data had incomect parity.

S4--Input data overrun.

A byte was received before the

CPU read the previous byte.

MFP failure or, less like1y,

GIue failure.

S5--No

GIue

IRQ.

CPU did not detect an interrupt by the,MFP. MFP or failure.

S6--Tra¡rsmit error.

MFP transnitter failed.

S7--Tra¡rsnit error interrupt.

An error condition was ereated intentionally to cause an interrupt, and

MFP didn't respond.

S8--Receive error interrupt.

intentionally to cause an respond.

An error condition h,as created interrupt, and the

MFP did not

S9-'RI/DTR connection.

Signal sent at

DTR is not detected at

RI.

SA--DCD/DTR connection.

Signal sent at

DTR is not detected at

DCD.

SB--RTS/CTS connection.

Sig¡al sent at

RTS is not detected at

CTS'

Mega

Service

Manual

3.

10

Testing

AUDIO

TEST

Outputs a low to channels.

One cycle high sweep on each of the three sound of each cha¡rnel is perforned. If a channel is nissing, replace the

PSG chip. If no sound is heard, verify the output of the chip wÍth an oscilloscope, the nonitor output connector.

If no and output trace the signal to the

PSG

Ís being selected by running the printer port or

RS232 test (these tests both select the

PSG).

from the

PSG, verify

TIMING

TESTS

These tests are run at power-up as well as being selectable fron the nenu.

Ttre

MFP timers, the

GIue tining for

VSYNC a¡rd

HSYNC, a¡¡d the

Menory tested.

Tt¡e video display

RAIII a¡rd verifies that

Controller test video display redirects display the correct addresses counters are nenory throughout are generated.

Odd patterns nay flash on screen as this test is run.

Tt¡ere are two tests which check the bus timing for the

1772 and PSG chips.

An error

Dessage is printed to the screen, then the test is run. If the test passes, occur and the

RS232 printed.

the the nessage nessage

1s erased. If not, a

Bus

Error will renain. If a terninal is connected to port, the nessage will not be erased, but

'rPass" will will be

TIMING TEST

ERROR

CODES

TO--MFP tiner error. not generate an

One or nore of the four tiners in interrupt on counting down the

MFP did

Tl--Vertical Sync.

GIue is not generating vertical- sync in the required tine period.

T2--Horízontal

Sync. Glue required time period.

is not generating horizontal s¡mc in the

T3--Display

Enable. Glue is not not generating an interrupt.

generating

DE output or the

IIIFP is t4--Video

Counter the correct addresses broken-up

Error. dÍsplay in

The for sone nenory the or all controller is not display.

This display nodes. generating will result fn

.- f ruu lt) a

T5--PSG Bus

Error.

Ttre

PSG chip is defective.

T6--L772 Bus

Error.

The

LlJ2 chíp is defective.

Mega

Service

Manual

3.11

Testing

\/o'

DMA TESTS

Four sectors

(2048 bytes) of data are h¡ritten to the

RAM on the port test fixture via high speed

DMA, then read back a¡rd verified. Tt¡is test Ís repeated nany tines for

RAIII addresses throughout the rarìge of

RAM.

DMA

TEST

ERROR CODES

DO--DMA tined out.

No

DMA occurred due to faulty

DMA

Controller,

GIue, or

Memory

Controller, or the

HDII{Î interrupt was not processed by the MF?.

The failure can be isolated by seeing

íf the

DMA

Controller responds to

HDRQ fron the test fixture with

ACK.

Verify the

MF? by seeing that the

HDII{T input causes an

INTR output fron the

MFP.

D1--DMA counter error. the nunber of bytes transferred was incorrect.

The Menory

Controller or

DMA

Controller is bad.

D2--Data nisnatch emor.

Ttre not the sa¡De as the data data received fron the

DMA port was sent.

Replace the

DMA

Controller. If the problen persists, check the data lines to the port for opens a¡rd

7lJ2 is shorts. loading the

A bus.

third possibility is that a defective

D3--DMA not responding. resquest

DMA controller could not respond to a data fron the external controller.

Replace the

DMA chip.

FLOPPY

DISK

TESTS

The Floppy Main

Menu

Floppy disk drive routine

(I{ARNING

-- all

1)

Quick Test choices except

2,6,7 write to the disk)

2)

Read

Alignnent

Disk

3)

Disk

Interchange Test

4

) oist< E;<erciser

5)

Check copy protect tracks

(80-82)

6)

Test

Speed

7) InstaII disk dríves

In single test noder a r¡enu is displayed showing seven options:

1.

Quick test.

For each disk installed, fornats, writes, and reads a¡rd tracks

0, L, rvrites track

79 and

79 of side

0. If double sided, fornats of side

1 and verifies that side 0 was not overwritten. If no disks are installed, checks to see what drives are online and if they are double or single sided.

To assure that the drive are correctly tested, the operator should install

(nenu option

6) before calting the test.

Once the test is run, the drives become installed, and will be size).

displayed on the nenu screen

(below the

RAM

Mega

Service

Manual

3.72

Testing

2.

3.

Read track.

Continuously with an analog alignnent input by the operator. a nunber, the default

If is reads a track, for diskette.

The track to be read nay be

"Return" track

40.

is checking alignment pressed without entering

Interchangeability test.

Checks to see if diskettes disk drives each can be read by the other disk drive.

fron two

4. Disk exerciser.

A nore thorough disk test; tests all sectors on the disk for a¡r indefinite period of tine.

5.

6.

7.

Copy some

Protect

Tracks.

Tests softrùare conpanies tracks

80-82, which are used by for copy protection).

Not all failures are cause for replacenent because sone nanufacturers disk drives will not write to these tracks.

Test speed. displayed acceptable on the lowest values measured key is

The rotational screen range is pressed.

as the period of rotation.

196-204 are speed of the drive

Ís tested nitliseconds. The híghest displayed.

The test stops when and

The and any

InstaII disks.

Specify how nany and what type of disks to test.

If nore than one test is selected from the nain nenu, the floppy nenu will autonatically.

not appear, but the

Quick

Test will be selected

FLOPPY TE.ST

ERROR CODES

No floppies connected--the controller cannot read

:Lndex pulses.

The cable nay be inproperly connected, or the clrive has no pohrer, or the drive is faulty.

F0--Drive not selected. resLore (seek

Drive was installed, but failed attenpting to track

0).

Check cornection of cables, pourer to drive. Verify the light on the front of the drive goes on.

Listen for the sound of the head seeking

(the slide on the diskette should

1772') should go open). If all this occurs,

TRO

(pin

23 on the

Iow. If so, check for an interrupt on pin

28 of the 7772. If none, replace the 1772. Else trace the interrupt to the

MFP, verify that the

MF? responds be asserting

INTR.

If the drive is not being selected

(no light), check the

PSG chip. Pin

20 should go low when drive

A is selected, and pin 19 should go low when drive B is selected.

If not, replace the

PSG.

F1,F2,Fl errors of previous versions nessage now says

"Error have been deleted.

The error liriting" (or reading or formatting), and displays a nore specific emor nessage,

€.8., "F9

CRC errortt.

Mega

Service

Manual

3.

13

Testing

F4--Seek error. Verify that t,l:e

1772 are the sent to the drÍve.

Probable failure in the

L772, but the drive is also suspect.

STEP,

MO, and

DIRC outputs fron

Fl--lirite protected.

Check the write

If 0K, verify that the ldP input during the test; if it is, then not, the problem is with the disk protect tab on the diskette.

(L772 pin 2l) is going the

1772 drive.

low

Is defective; if

F6--Read compare supposed error.

Data to be written. read from

Check the disk was diskette, disk drive,

L772, and

DMA

Controller.

not what in the following was order:

F7--DMA

FDRQ error.

DMA.

DMA

Controller

Replace the

DMA whÍle running the high with each data byte could not respond to a request for

Controller. If emor persists, check test. It should nornally be low and go transfemed. If stuck high, push the reset button a¡rd verify that

MR

(L772 pin 13) goes low. If not, trace

RESHI to its source. If

MR is 0K, but

FDRQ is still stuck, replace

E}r'e

1772.

F8--DI{A count error.

Replace the

Memory

Controller, not fix it, replace the

DMA

Controller.

if that does

F!--CRC error.

The diskette or disk drive nay be bad, else replace

Ehe

1772.

FA--Record be a not bad found.

The L772 could not read a sector header.

May not

A).

diskette, drive or L772. If the test. fails drive

A but not drive B,

Ehe

1772 is not at fault

(likewise fails

B

FB--Lost data.

Data was

1772 could tra¡rsfer passes, also be the tJl2 is at fault.

transferred to the

DMA

Controller. If

DMA

Port test probably to bad. t}:e

The

L772

DII{A faster than

Controller the could

FC--Side select emor--single both sides sided to be overwritten.

drive.

The test tried to write of the diskette, but writing side

1 caused side

0

FD--Drive not ready.

Probably

Could a bad also be a

The disk faulty fornat/write/read drive.

L772.

Verify by operation checking timed-out.

another drive.

Soft Error

= does not cause a failure after

1 retry. (If doesn't fail a second time.

)

Hard

Error

= failed second retry.

Unit will halt if you reach any of the following:

20 read errors,

20 write errors or

! fornat errors.

Mega

Service

Manual

3.

14

Testing

PRII.ITER AND JOYSTICK

PORT

TF"STS

The port test fixture is used to test the paralle1 printer port and joystick ports.

The parallel port test writes to a latch on the test fixture and reads back data.

The joystick port test outputs data on the parallel port, which is directed through the test fixture to the

Joystick ports. The keyboard reads the joystick data in response to connands from the

CPU.

The cables connecting reversed, or the joystick ports to the test fixture nust not be the printer and joystick tests will fail.

PRTNTER/JoYSTTCK ERRoR

CoDES

Po--Printer port error.

Data read fron the printer port was not what was written. Verify that the data lines on the

PSG chip

(pins

6-13) are toggling when the test is run. If not, run the

RS232 test. If the

RI-DTR and

DCD-DTR errors occur, the chip is probably not being selected.

Check if the chip

- selects are being activated and the

2ütlz cLock is present. If the

PSG is selected and not outputting signals, replace it.

If the data lines toggle, verify continuity.

AIso verify that

J1l

(Joystick

0) pin

3 is pulled up. Verify the test fixture is good by testing another conputer. If it is

0K, replace the

PSG.

P1--Busy input error.

The input to the

MFP is not being read, or the

STROBE output fron the

PSG is not functioning, or

Joystick 0 pin I is not connected.

If the P0 error also occurs, see handling for that. Othervise, look for a signal amiving at

MFP pín

22 fron

J5 pin 11. If no signal at

J5, the test fixture may be bad. Verify with another conputer.

JO--Joystick

Busy

Port input

0.

Ttre keyboard input is not functioning. If the error occurs, fix that first. othervise, replace the keyboard.

If error persists, check continuity fron

J11 pins 1,2,3,4 to ltZ pins

12,10,9,8 respectively.

Jl--Joystick Port 1.

The keyboard input is not functioning.

If the

Busy input error occurs, fix that first. otherwise, replace the keyboard.

If error persists, check continuity fron

J11 pins

1

,2,3,4 to ttZ pins J,5,4,1 respectívely.

J2--Joystick time-out. Joystick inputs rdere si¡rulated by outputting data on the printer port and routing Ít via the test fixture to the joystick ports. Joystick inputs are detected by the keyboard and sent to the

CPU via the

68¡0.

This error ca¡¡ be caused by printer port failure (code

P0), keyboard faílure, keyboard-CPU connunication line, or a faulty test fixture. If the porter-up keyboard test passes, this elininates any problen with keyboard-CPU communication.

Mega

Service

Manual 3.r5

Testing

J3--Left button input. If Pl emor occurs, fix that first.

0therwise replace continuity from J10 the keyboard. 0n the pin 6 to ltZ pin

11.

520ST, also check

J4--Right button input. If Pl emor occurs

, fix that first.

Otherwise replace continuity fron

J10 the keyboard. 0n pin 6 to

JtZ pin

6.

the

520ST, also check

HIGH

RESOLUTION MONITOR

If this test is selected while a color monitor is connected, a message waits received is displayed to connect the nonochrone

(the operator connects the nonochrone nonitor.

The

CPU for an interrupt from the

MONOMON input to the

MFP, and when nonitor), changes the dÍsplay to high resolution.

Ttre display screen shows horizontal and vertical lines, each

2 pixels in width.

Ttre screen will reverse every two seconds. ltlhen the operator sees the display is correct, he unplugs the nonochrone nonitor and re-connects the

RGB nonitor a¡rd the display should return to nornal.

GRAPHICS

CHIP

(BLiTTER)

This appear on

(G0-G13)

, tests around and perform the the abÍIity of the

BITBLiT to

Eove blocks of nenory logical operations on the data. No patterns screen.

Ma¡ry different error messages are possible but the action for any emor is the chip.

A faulty

BLiTTER may cause a

BUS

ERROR.

sa¡ne: replace the

REAL-TIIúE

CLOCK

The test saves the current time and date, and writes a new time, waits one second, and verify all registers.

verifies that hours, minutes, seconds, etc. have all rolled over.

The is repeated for a¡rother date to

EXPANSION

CONNECTOR

This test, for

Mega modeJ.s, requires the expansion test fixture

(the top cover and shield must be renoved to install

Èhe test fixture). It tests the expansion interface, in part by software, and the renainder by LEDs.

The data and address busses and interrupt lines are tested in software.

The control lines fron the

CPU are tested with the LEDs.

Most of the

LEDs will go off after the systen is turned on and the

Inenu appears on the screen.

Three

LEDs

BGACK

(bus expansion will remain connector lit: grant acknowledge).

These should go test is

BR

(bus run request), and

(2)

BG either

(bus grant) off after (1) the

DltIA test and the or floppy test are run.

The

LEDs sinply indicate that the line is toggling.

A lit

LED neans the line is not changing.

Mega

Service

Manual

3.t6

Testing

/

¡'')

,t u¡ò1 i4

"¡4 tJ

The software tests three groups of signals: data bus, address bus, and interrupts.

The first test writes and reads the

RAM on the test fixture, setting one bit high at a tine, to check for open or shorted data lines. If an error is found, the nessage

"EXO bad bit" is displayed.

The second test writes an increnenting pattern (0,1,2,...1

across address bits O-1!, then across address bits

16-23 to the

RAM on the test fixture to check for open or shorted address bits.

If an error is found, the message

"EX1 external

RAM error' low byte" or

I'EX2 external

RAM emor, high byte" on whether the is printed, depending error occurred in the low or high address.

The create third test uses circuitry on the external test fixture to interrupt requests. There are three interrupts:

Il.¡T3, IlfT5, and INT7. If the appropriate interrupt does not occur when expected, then a nessage

Ís displayed:

"EX3

INT3 error,

"EX4

INT5 errort', or ttEXl INTJ errortt.

ERROR CODES

QUICK

REFERENCE

Ttris is a brief sunmary of all error code which nay occur when running the diagnostic.

INITIALIZATION

(Errors occurring before the title and menu appear)

11

RAM data line is stuck.

L2

RAM disturbance. Location is altered by write to another location.

13

RAM addressing.

Wrong location is being addressed.

14-

MMU error.

I5

.

RAM sizing

No

DTACK error. after

RAM access.

Uppernost address faiLs.

T6-

5 V*,

EXCEPTIONS

(may occur at any tine)

El--E5 not used

E6

Autovector error.

IPLO is grounded or

68000 is bad.

E7

Spurious interrupt.

Bus error during exception processing.

Device interrupt vector.

interrupted, but did not provide

EB

Internal Exception

(generated by

68000).

E9

Bad

Instruction

Fetch.

EA

Address error. Tried to read an instruction from an odd address address.

.--EB or read or write word or long word at an odd

Usually this error is preceded by a bus emor or bad instruction fetch.

Bus error.

Displays

Generated the address of the internally device being by the accessed.

68OOO or externally by GJ-ue.

Usually caused by device not responding.

tr rrirl-

6 LU

!

Mega

Service

Manual

3.17

Testing

RAM

R0 Emor in low nenory (first

2K), possibly affecting program execution.

Rl

Error in

RAM chip.

R2

Address error.

Bad

RAItl chip or memory controller.

Address line not working.

R3

Address error at

64k boundary.

R4

Error during video

RAM test.

Bad

RAM chip.

KEYBOARD

K0

Stuck key

K1

Keyboard controller is not responding.

KZ

Keyboard controller reports error.

MIDI

M0

Data not received.

Ml

Data received is not what was sent.

M2

Data input franing error.

M3

M4

Parity error.

Data overrun. byte arrÍved.

Byte was not read fron the

68!0 before next

RS232

S0

Data not received.

51

Data received is not what was sent.

52

Data input franing emor.

53 Parity error.

54

Data overrun.

Byte was not read fron the

MF? before the next byte arrived.

55 IRQ. Ttre

MFP is not generating interrupts for tra¡rsmit or receÍve.

56

Tra¡rsnitter error--MFP.

57

No interrupt fron transnit error

(MFP).

58

No interrupt from receive error

(MFP).

59 DTR--RI.

These signals are connected by the loopback connector.

Changing

DTB does

5r''

SA

DTR--DCD.

Same as 59 for these signals.

> not cause change il

SB

RTS--CTS.

Sa.ne as 59 for these signals.

in

RI.

DMA

D0

Time-out.

DMA did not take place, or interrupt not detected.

Dl

DMA count

eror.

Not

aII

bytes arrived.

Possible

Menory

Controller error.

D3

DMA

Controller not responding.

Mega

Service

Manual 3.18

Testing

TIMING

T0

MFP timers failed.

T1 Vertical sync timing failed.

T2 Horizontal sync tining failed.

T3

Display

Enable

Interrupt failed. ltt - ¡r--^\

T4

Menory

Controller video address counter failed

.

4'^

ö b i' a

T5

PSG

Bus test.

PSG chip is causing a bus error by staying on the data bus too long.

wJ

'

T6

1J72

Bus test.

L772 chíp is causing a bus error by staying on the data bus too long.

PRINTER AND JOYSTICK

PORTS

P0 Printer port error.

Pl

Busy

(printer port input) failed.

J0

JoysÈick port 0 failed.

J1

Joystick port

1 failed.

J2 Joystick

(keyboard controller) timed-out.

J3 Left button line failed.

J4

Right button line faired.

FLOPPY

DISK

DRIVE

FO Drive offline.

Not responding to restore (seek track

0).

F1

Format error.

(Note: former

F2,F3 now specific write and read emors are deleted.

The nessage will say "error writing" [or error found.

) reading] and display the

F4

Seek emor.

F5 ['irite protected.

,F6

Data conpare.

(Data read not equal to data written.

) n

DMA error.

FB

DMA count error

(Menory

Controller counLer.

)

F9

CRC error.

FA

Record not found.

FB

Lost data.

FC

Side select error.

FD

Drive not ready.

Tined-out perforning the command.

Mega

Service

Manual 3.r9

Testing

SECTION

FOUR

DISASSEMBLY/ASSEMBLY

MEGA/ST

DISASSEII{BLY

Top Cover

Removal:

1)

Renove keyboard connector fron the side of the top cover.

2)

Turn unit upside down.

l) Renove the 9 screws fron the square holes.

These fasten the top case to the bottom. If the printed cÍrcuit board is to be exposed, or the disk drive is to be renoved, also renove the three screws the disk drive Ín place.

fron the round ho1es.

Ttrese hold

4) Turn the unit upright. l{hile lifting the top cover up stightly fron the back, unplug the battery connector fron underneat renoved its left rear corner. easily.

Now the cover can be

Upper Shie1d Renoval:

1) Straighten the six twist tabs.

Note that there ís one located under the disk drive.

2) Lift the shield up fron the back gentlely so that it will be free from anythings in the rear.

3)

Push the disk drive up while lifting up the front of top shield out of the botton cover and pull forward.

Disk Drive

Removal:

1) Lift the disk drive slightly and unplug the power harness connector and the ribbon cab]e.

Power

Supply

Removal:

1)

Remove the 2 screws at front corners of power supply.

2)

Unplug the wire harness connector in the right front corner of the poh,er supply.

3) Lift the poh,er supply up out of the main assenbly.

Mega

Service

ManuaÌ

4.r

Disassenbly/Assembly

Renoval of main assenbly fron botto¡n case:

1) If power supply has not already been renoved, then follow the power supply renoval section to renove it.

2)

Renove the six studs whÍch secure the I/0 shield to the botton case.

3) Lift the assembly up from the front and pull fon¿ard.

Renoval of

Shield Fron

Printed

Circuít

Board:

1)

Straighten six twist tabs.

It nay be necessary to pull the twist tabs away fron the board slightly.

2)

Renove the

I/0 shield in the back.

Note:

Now convenient that the najor conponents are exposed, this is a for troubleshooting.

The keyboard a¡rd disk drive may be re-connected side if configuration those components are needed.

and placed off to the

3) Lift the printed circuit assenbty away fron botton shield.

I'tega

Service

Manual

4.2

Disassenbly/Assenbly

Mesa/ST

RE-ASSEMBLY

1)

Place insulation panel on botton shield.

2)

Attach the I/0 shield to the

I/0 ports.

Place Main

Board on top of

Botton Shield over insulator panel.

3) Place the assenbly

Ín lower plastic case.

4)

Secure the

I/0 shield to the botton case with the 6 studs.

5) PIuS in power supply connector and position porr¡er supply with tabs in slots.

6) etace assenbly in lower plastic case.

7) Fasten the power supply to the botton case at both front corners supply with shield tno screws. Tttis in hold the scree,, place, or by using a renoving car¡ be done magnestized the shield.

with the power screwdriver to

8)

Plus disk drive power and ribbon cables into drive

(cables go under shield), and position drive over standoffs.

t) Push the battery corìnector up fron the opening located in the left rear corner of the top shield.

10) A1ign tabs on bottom shield with slots on top shield and fit top shield over nain assenbly. Twist the tabs to lock in place.

11)

Place the top cover over the assenbly.

12) Turn over longer screhrs drive.

the assenbly and go into the replace round the 9 screws. holes to

The secure the three disk

A h¡ORD

OF

CATITION

It is strongly reconnended that the conputer be retested once in plastic to nalce sure that the re-assenbly was done correctly and there are no shorts to

Shield.

Mega

Service

Manuaf

4.3

Disassembly/Assembly

I

I

SECTION

FIVE

SYMPTOM

CHECKLIST

This section gives a brief summary of comnon problens and their nost probable

óauses. For nore detail, refer to the section on troubleshooting in this

Troubleshooting Guide.

docunent, of the Diagnostic

Cartridge

Sympton

Probable

Cause

DISPLAY

PROBLEMS

Black screen

No power (check LED), bad GIue chip, bad Video

Shifter.

See TESTING section,

"Troubleshooting a

Dead

Unit".

White screen

Video

Shifter, Glue,

Menory

Controller, 68000. Use

Controller, diagnostic

DMA cartridge with terninal connected via

RS2l2 port.

Dots/bars on screen

One color nissing

RAM,

Menory diagnostic

Controller, cartridge.

Video

Shifter.

Use video sunner, buffer,

Video

Shifter.

Check signals

$rith oscilloscope.

Scra.nbled screen

T.V. output bad

Glue,

Menory

Contro1ler.

Use the diagnostic cartridge.

Ir{odulator, phase locked with your oscilloscoPe.

loop.

Trace the signal

DISK DRIVE

PROBLEMS

Disk won't boot

Power supply,

FDC

(1772),

DMA chip, disk

Controller,

PSG drive.

See if select light goes on' if not, check

PSG outputs. Listen for

Eotor spinning.

If not, disk drive or try check working, check DMA the diagnostic cart.

an the power external

Controller supply. drive. If and L772

Swap not with

Disk won't fornat

Systen crash

Ioading files after

FDC(1772),

DMA

Controller, disk drive.

Diskette, disk dríve,

FDC

ß772), DMA, ot

Menory

Controller.

Swap diskette, retry.

Use the âiagnostics to check

FDC

(L7721,

DMA

Controllèr,

Menory

Controlleri drive.

or replace disk

Mega

Service

Manua1

5.7

Synptom

Checklist

Systons

Probable

Cause

KEYBOARD

PROBLEMS

Keys won't

work

Bad keyboard

controller,

6850,

MFP.

Keys won't but nouse

work

Keyboard

cable

was

inserted white unÍt

was

does

powered, recycle power.

UIDI

PROBLEIUS

No

data

Bad opto-isolator

,

74LS05).

chip,

6850,

inverter

(74LS04

RS232

PROBLEMS

No

data

Bad 68901

MFP, receiver,

driver,

or

PSG chips,

+/-

12v supply

is blown.

Use diagnostics to lsolate bad line(s).

PRII.ITER

PORT

PROBLE}IS

No output

Bad PSG,

MFP chips.

Does not output

Input inpedance of printer is less than lK ohn to a specific

,nodify pullup resistors on printer.

printer

DMA PORT

PROBLEMS

Does not function

Bad

DMA

Controller,

Menory

Controller,

L772

(loading the bus).

REAL TIME

CLOCK

PROBLEMS

Does not function

Bad

RTC

PAL chip, clock chip, crystal.

Does not save after cold boot tine

Bad batteries, power off sense circuit.

BLiTTER

PROBLEMS

No vídeo when is inserted

Blit

Junpers below a¡rd to right of blitter chip nust be cut before blitter will work.

Does not functÍon

Replace blitter chip if above step doesn't fix problen.

Mega

Service

Manual

5.2

Synptom

Checklist

SECTION

SIX

DIAGNOSTIC FLOII¡CHARTS taken

The in

This sectÍon sumnarizes in diagra.natic forn the steps troubleshooting the details of using

Mega using the cartridge are the not diagnostic sho$m; this cartridge' shows the context in which the cartridge would be used, including sone problems

ôartridge for which the cartridge would not be useful.

Usage of the is covered in the troubleshooting guÍde.

In general, the user would run all the tests, look up errors in the troubleshooting guide, and take the action reconnended.

Atthough necessary a thorough understanding of the syste¡n may be in solving sone problens, in most cases following the flowchari, reading the docunentatíon on the diagnostic cartridge where necessary, and swapping out the indicated conponents will result in repair of the

Problem.

Replacement Procedures where replacenent is indicated, replace the conponent

(if more than one is indicated, replace one at a time) with a kno*n good whether part. If the other first part is system has been rePaired.

components good by are later replaced, verify replacing in the systen once the

Handting of

Integrated

Circuits

Extreme care should be taken when handling the integrated circuit chips.

They are very sensitive to static electricity and can easily be damaged by careless har¡dling.

Keep chips in their plastic carriers or on conductive foan when not in use.

Mega

Service

Manual

6.t

Diagnostic

Flowcharts

START

CONT\ECT TERM¡NAL

TO

RSæ2

PORT

CYCN-E

POWER

DISPLAY ON

TEFINô.¡AL ?

DAGNOSTIC

IS

DISPI.AY

RE.ADABLE ?

REPLACE PARTS

PER

DIAGNOSTIC

GI,JDE

FEPLACE PARTS

PER

DIAGNOSTIC

GUIDE

CYCLE POWER

RI.}.¡ ALL TESTS

ERROR?

OTHER?

Mega

Service

Manual

MEGA/ST DIAGNOSTIIC FLOtll

CHART

6.2

Diagnostic

Flowcharts

NO

ERROR ON

DAGNOSTIC

RUN

DISK

DAGNOSTIC

OR

REPLACE

DRIVE

TRACE

SIGNAL

FROÌ\, VDEO

SHFTER

TO

OTJÏPUT

RUN

APPROPRIATE

TEST

CONTINUOUSLY

PROBLEM

FOLAD

?

CON¡TACT

ATARI

TECHNICAL

SUPPORT

Mega

Service

MEGA/ST

DTAGNoSTTTC FLoW

CHART

6.3

Diagnostic Flowcharts

NIO DISPLAY

ON

ìvlOÀtTOR

OR TEruINAL

\ t/t/

t€

1.

CI€q<

SHIFTER

2. REPLACE

OSCILLATOR

TN

\'

FEIVIOVE SHIELD

NSPECT

PCB

TEST

FOR

SI-{OFITED + 5

V

FEPLACE

POWER

SUPPLY

t€

FEPLACE

GLUE

1.

2.

FIEPLACE:

GLUE ltlBMORY

CONTROL

3.

CPU

YES

Fts232

DISPLAY

?

DAC¡l'.lOSTlC

1.

SEE

THEORY

OF

OPERATIO¡¡

2

REPLACE

PCB

3.

COf..¡TACT ATARI

SUPPORT

Mega

Service

Ma¡rual

REPLACE PARTS

PER

DIAGNOSTIC

GUIDE

6.4

l€

REPLACE

PCB

FEIVIOVE Sl-lORT,

RE€HECK

Diagnostic

Flowcharts

NO

DISPI.AY,

Ì\¡O ERROR

32 ¡úHZ cLoo<

?

REPLACE

XTAL

RESTART

REPLACE

SHFTER

OTJTPUT

FROM

SI-IFTER

TRACE OUTPUT

TO COI\¡€CTOR

FìEPLACE

FAT-}G

PART

RESTART

Mega

Service

Manual

REPLACE tì/EMORY

CONTROLLER

MEGA/ST

DrAGNoSTrrc

FLow

CHART

6.5

RESTART

Diagnostic Flowcharts

SECTION

SEVEN

PARTS

LISTS

AND ASSEMBLY

DRAWINGS

Mega service

Manual 7.I

Parts

List

& Drawings

MEGA

PARTS

LIST

PART

NUMBER cA200055-00

1 cA200093-001 cA200008-001 cA200018-001 cA200022-001 cA200025-00L cA200039-001 cAz00040-001 cA200041-00L cA200042-001 cA200043-001 cA200054-00L c070350-003 c070352-003 clû3047-001 cAo70025

DESCRIPTION

PCBA

(l¡le

no¡¿)

MEGA

4

PcBA

(1Me no¡¿)

MEGA

2

MEGA

POWER

MEGA

2/

SUPPLY w/FAN

4

CASE

BOTTOM

MEGA

MEGA

2

CASE

TOP

4

CASE

TOP

MEGA KEYBOARD COMPLEÎE

MEGA KEYBOARD

MEGA KEYBOARD

CASE

TOP

CASE

BOTTOM

MEGA KEYBOARD

CONNECTOR PCBA

MEGA KEYBoARD (on¡r,y)

MEGA KEYBOARD

CABLE

FDD

FDD

FDD

uNrr uNrr uNrr

(1v

(r¡4

(ru cAP 100pF 50V t5%

50v

50v

eyre) ayrn)

STM1

MOUSE

ASSEMBLY cAP 30pF

CAP cAP

1000pF

25v +202 cAP

50v

+5%

39pF 50V t5%

CAP

150pF cAP 330pF

0.1pF t5% tl-Oå

25v2.

r,¡nwrRoNrcs cHrwor.¡ cHrNo¡¡

cH. cH.

cER cER

SL. cH.

cER

B. x.

AXIAL

AXIAL cER cER

AXIAL cER AxrAL

AXIAL cER

AXIAL

AXIAL cAP

O.221tE

CAP cAP

0.47¡:F

4.7pF

50v z5U.

25v

25V

ELEC cER z.cER

AXIAL

AXIAL

AXIAL cAP 10pF

16V

ELEC AXIAL cAP

47ytF

16V

ELEC RADIAL cAP

100pF 16V

ELEC AXIAL cAP

1000pF L6v

ELEC AXIAL cAP

4700¡rF

L6v

ELEC

RjADIAL cAP

L00L¡rF

16v

ELEC RADIAL cAP 5-30pF

TRIMMER

RES O

OHM

JUMPER

RES

RES

RES

5.1

oHM

L/AW

5%

CARBON

27

OHM

T/4W

5%

CARBON

33

OHM

L/AW

5å

CARBON

RES

RES

47

OHM

L/4W

5å

CARBON

75

OHM

L/AW

5%

CARBON

RES

1OO OHM

RES

L/4W

5%

CARBON

].50

OHM

L/AW

5%

CARBON

RES

RES

RES

220

OHM

470

OHM

L/AW

I/AW

5%

5%

CARBON

CARBON

].K

OHM

T/AW 5%

CARBON

RES

1.2K

OHM

L/4W

59"

CARBON

LOCATTON

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUBASSEMBLY

SUB FOR

ABOVE

SUB FOR

ABOVE

ASSEMBLY c39,40 c54 c43-46 c28 c29 c68,69 cL,2,5-7 ,9-2L,23,26

27

,30-33,36,38,4t,

42

,47,49,50

,52 ,55

,

56,57, s9,60 ,64-66

,

70

,73,LL2,113

L2L-L23 c80-95 c67

,t20

, c22

,

24 c3 c34,35 c8

,

37 cL40

,25

,51 c4 c49 c53

Rl20

,L23,L26,L45,

146,DL2-L4,w2,3

Rl5

R83

R52

,54 ,55 ,57

68,76,110,l_13

,60-66

R45-48

R67,73 ,77

R69

,

75

R23,115

,78, 86

,

116

Rl0

,

L4

,L6 ,17 ,Lg ,44

R26

Rl,2

,4,2t,24,30

,37

38,40-43,82,85,111_

R20,76

PART

NUMBER c070567-004 c070

1

59

-00

6 c070

448 c014384 c070205 c070471 -001 c07047L-002 c0?0790

c07024L-002 cl01805 c025993

cll0232

c1

00281 c010L29 c070130 c070131 c070134 c070033 c070445 c070644-0

L

1 c10028

3

-00

1 c070120 c070119 cAO70024 cAo70023-003 cA200053

-002 c]_01_643 c025982 c025913 c025915 c0259L4 cl0

160 c0259L2 c025986

I c025981 c025983 c025984 c025985 cr0L7t2 c025988

DESCRIPTION

RES

2.2R

OHM

].

/ 4W

RES

52

CARBON

3.3K

OHM

].

/

4W 5%

CARBON

RES

RES

RES

4.'7K

OHM

1.

/ 4W

5Z

CARBON

5.1K

OHM

1/4W

5Z

CARBON lOK

OHM

L/AW 5%

CARBON

RES

12K

OHM

L/4W

RES

51.K OHM

T/ 4W

5%

5å

CARBON

CARBON

RES

NET!{ORK

RES

NETWORK

RES

NETWORK

INDUCTOR

INDUCTOR

INDUCTOR

INDUCTOR

lK

OHM

4.7K lOK

X

OHM

OHM

6

X

X

LINE

FILTER

NOISE

FILTER

ZJS5lOL_02

8

8

FERITE

BEAD AXTAL

O.27UA 20% AXIAL

L0pH 10% AXIAL

220¡tH L0% AXIAL

TRANSISTOR 2N3904

TRANSISTOR 2N3906

DIODE

1.N9].4

DTODE

].SS1O8

SCHOTTKY BARRIER

CRYSTAL

2.4576

MHZ

CRYSTAL

CRYSTAL

CONN

32.768RH2

32.0424

MHZ

40

PTN RIGHT

ANGLE

CONN

CONN

CONN

CONN

CONN

DB-19S

HARD

DISK

L4

PTN DTN FLOPPY

DISK

DB-25P

RS232C

DB-25S

PARALELL

13

PTN

DIN

VIDEO

5

PIN DIN

MIDI

CONN

CONN

CONN

SINGLE

DOUBLE

CONN

DOUBLE

SOCKET

40

PIN

SOCKET

SOCKET

INLINE

INLINE

28

PIN

68 PIN

LCC

6

PIN

24

PIN

INLINE

MALE

64

PTN

PUSH SWITCH

FLAT

CABLE

CABLE

34P

ASSEMBLED

4P

ASSEMBLED

2

PIN

CABLE ASSY:MALE TYPE

IC

CUSTOM

ST

BLITTER

rc

68000-8 cPU

IC

CUSTOM

DMA

CONTROLLER

IC

CUSTOM GLUE

IC

CUSTOM

SHIFTER

IC

CUSTOM

FULL

SHTFTER

(W/D/A)

TC

CUSTOM

MMU

IC

1489

RS-232C,

RECEIVER

IC

1488

RS_232C,

DRIVER

fC

YT42L49

,

SOUND

IC

68901,

MFP

IC

6850,

ACIA

IC

DYNAMIC RAM

1M

X

1

IC

PC9OO PHOTO COUPLER

LOCATION

R5

R27

R6,1L,28

,29 ,39 ,LLz

R22

R7 ,8 ,25

L09,114

,33-36

,

108

,

R18

R32

Ro7 nþr

-q

RP5

LL

,6

,L2

,45

,46 ,48

L47

L50

L5

L9

L2-

4

-30,32-43

,24

Q1,3,6-10

Q2

D1-3,5-8,15-18

D4

Y1

Y2 oscl

J2

Jl0

J13

J7

J6

Jl4

J3

,4

Jl,18

JL7

J15 v27 ,3L u3,4

,6 ,7

,9,10 u5,

17,30

S1

JL2

Jl1

J9

U5

U8 v27 u17

U31 u31 u30 ul9 v20 or u16 u18 u],4,15 u40-55

(

60-7s

) u13

PART

NUMBER cL0L62t cL0L622 c101.625

co1044'l c026028 c10

1629-00

1 c101

630

-00

L c070349-002 cl00296-00

L c070322 c070323

DESCRIPTION

LOCATTON rc rL

7705A rc

74Ls02,

QUAD

NOR

IC

74LSO6,

HEX INVERTER O.C.

IC

74LSO7,

HEX

O.C.

BUFFER'

rc

74Ls32,

QUAD

2-TNPUT OR

GATE

IC

74LS]-48

8-3

PRIOR

ENCODER

rc

74Hc00 guAD

NAND

GATE

IC

RP5C15 REAL

TI¡,IE

CLOCK

IC

RTCPAL PAL16L8

TC

TC

74L5244.3

STATE

LINE

BUFFER

74LS373

LATCH

IC

74LS].]. TRIPLE 3-INPUT

AND

GATE

IC

TL497A

SVIITCHING

REGULATOR

TC

WD-L772

FDD

CONTROLLER

IC;

TOS

ROM

1

MEG

HI-O

IC;

TOS ROM

1

MEG

LO-O

AC

POVTER

CORD

(Ur,zCSe)

MEGA

MANUAL

OWNERS

COLLAR

A

COLLAR

B ul.

U2L v26

U2 u78 u39 v24 u25 u37 v32 u33 vL2

,35 ,58 ,59

,36 tJ22 v28

U9 u10

3

DRIVE

SPACERS

1

DRIVE

SPACER

Ql,^

:o

G)-

I

ATAnl ÍJAPAiN

COßPORÂNOT¡

,/l\ t-"..-; x'vor¡, Bu'd,m s filfiPl' a-:ro rdamffi

M'nâbku. rdp t6 r4A//,/ ASSY l4EGA

Stur:

D*rst\r.

\rt c

! \t¡ NONE

- iÍr

_)c

srtd 3 0t 3

æ

I'f

I

I

I

I i\ c

I

I

?;

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GLOSSARY

SECTION NINE

OF PART

NAMES AND

TERMS

BITBLiT--Atari graphic used chip which is actually a

DMA device. It is to tra¡rsfer block of memory from a source to destination with the patterns and a combination of any logical operations between transfer.

source and destination which was set up prior to the

BUS

ERROR--GIue has asserted

BERR there to inforn the processor that is a problem with the current cycle.

This could be due to a device not responding

(for exa.nple,

CPU tries to read memory an but the

Menory

Controller fails to assert

DTACK), op illegal causes access

(attenpting exception processing.

to write to

ROM).

A bus error

CPU--the

68000 microprocessor.

DMA--direct

¡nenory access.

Process from external storage device in which data is tra¡rsferred to

RAM, or from

RAM to external storage.

Transfer is very fast, takes place independent of the

CPU, so the

CPU can be processing while

DMA is taking place.

Glue arbitrates the bus between the

CPU ar¡d

DMA.

DMA

CONTROLLER--Atari process. proprietary chip which controls the

DMA

All disk I/0 goes through this device.

EXCEFIION--a state in which the processor stops the curent activity, saves what it will need to resune the acbivity later in

RAM, fetches a vector (address) from

RAIft, and starts executing at the address vector.

When the exception processing doing before by detail.

is done, the processor will continue what it was the exception occurred.

Exceptíons can be caused intemupts, instructions, or emor conditions.

See also

Section Two,

Systen

Errors, or a

68000 reference for nore

GLUE--Atari proprietary chip which ties together aII timing and control signals.

system

HALT--state j-n which the

CPU high-inpedence is idle, all bus lines are in the state, and can only be ended with a

RESET input.

This is a bi-directional pin on the

CPU.

It is driven externally by the

RESEtr circuit on power-up or a reset button closure, and internally when a double bus fault occurs.

A double bus fault is an error during a sequence which is run to handle a prevíous error.

For sxamplê, if a bus emor occurs, and during the exception processing for the bus error, another bus error occurs, then the

CPU will assert

HALT.

Mega

Service

Manual 9,1

Glossary

HSYNC--timing signal for the video display.

Deternines when the horizontal ðcan is on the screen, and when it is blank iretraci.ns).

The synchronization (approx' every

63 microseconds) also is encoded onto IPL1,2 as an interrupt to the

CPU.

II,ITERRUPT--a request by a device for the processor to stop h¡hat it is doing a¡rd perforn processing for the device. It is a type of exception. they will

Interrupts be ignored if are they naskable do not in software, meet the current neaning priority tevèl of the

CPU.

There are three priorities: the highest are

MFP interrupts, then

VSYNC interrupts' and lowest are

HSYNC interrupts. Interrupts are signaled to the cPU on the

Interrupt Priority

Level inputs (IPL0-2). see

Theory of

Operation, Main System, MFP, and Glue.

MEMORY

CONTROLLER--Atari accesses.

Subsysten for details.

proprietary chfp which ha¡rdles all

RAM see

Theory of operation,

Main systen a¡¡d video

MIDI--Musical

Instrunent

Dígital Interface.

An electrical standard by which electronic instrunents comnunicate.

AIso, the lógical sysgen for such comnunication.

In the

1040ST, consists of a

6B50 interrupt channel.

connunications chip, driver and receiver chips

(74LS04,

74LSO5, and PC-900 photocoupler), and an

MFP

MFP--MuIti-function

Peripheral, atso

68901.

Interrupt control, timers, and usART for

RS232 connunicatÍon. see Theory of

Operation, Main

System.

MODULATOR--device

HSYNC into which combines a conposite video s:'.gnal signals

R,G,B'

VSYNC, for nonitors requiring typeinput,andalsomodulatesthissignal,combinedwith audio, onto a¡r RF camier for output to a television.

and this

PHASE LOCKED

LQOP--circuit which locks the horizontal sync signal onto the color burst reference frequency for accurate color on the unstable, may

T.V. lrJithout this circuit, colors on the T.V. become flickeríng or shiftÍng about on the screen.

The

PPL be on a daughter board located in front of the video shield or hand wired onto the naÍn board within the video shield, or

(possibly) in later versions, integrated into the printed circuit board.

PSG--Progranmable

Sound

Generator, also

YM2149. Yanaha version of

Genéral Instn¡ments

AY-3-8910. Has two three sound channels. used

I Uit I/0 ports in parallel port and audio.

and

Rs232c--Electical standard the physical and for serial digital comnunication.

AIso logical device which perforns comnunication using this standarã. In the

ST computers, consists of the

MFP, PSG,

1488, and 1489 cniPs.

Mega

Service

Manual

9.2

Glossary

L772--Western

Digital

Fl-oppy

Disk Controller.

6850--atso

AcrA

(Asynchronous connunication rnterface

Adapter).

rnterfaces between B bit pararlel bus and serial communication keyboard bus. In the conmunication, and

ST, one there are for thro

6850s,

MIDI conmunication.

one for

6890t--see

MFP.

SUPERVTSOR

MoDE--state of the cPU in which it is arlowed to access alr hardware a¡rd

RAM locations, and perform sone priviriged instructions.

Deternined by the state of a bit in the status

Register.

The operating system operates in supervisor node, and switches to user mode before passing control to an apprication

(although the application ca¡r enter supervisor mode if it wishes).

usER

MoDE--state of the cPU in which certain instructions a¡rd areas in the memory nap are disallowed (resulting in a privilege violatÍon exception if attempted). See also

SUPERVISOR

MODE.

vsYNC--signal used for vertical synchronization device.

Occurs aE

70

Hz (monochrome), of cRT display or

50 or

60 Hz color.

l¡M2149--see

PSG.

Mega

Service

Manual

9.3

Glossary