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HOW TO INSTALL 3.5" STANDARD IBM FLOPPY DRIVES IN A RADIO SHACK MODEL III OR MODEL IV
My goal is to get two 3.5” Standard IBM Style Floppy drives working on my Model IV, without modifying the actual 3.5” drive.
I have decided that it would be acceptable to modify the existing Floppy Interface cable, or make a new one. Temporarily, I have modified an old Edge Connector to 34 Pin DIN Adapter for my initial testing. (Basically I just lifted the following Pins on the
Adapter : 2, 10, 12, and soldered a 1K OHM Resistor from Pin 1 to Pin 2, making the perfect Drive 1 test adapter. Drive 0 will require further modifications as shown later in a detailed image.)
The Radio Shack Model III & IV Floppy Disk Controller (FDC) has the following Signals routed to Connectors J1 (EXTERNAL) and
J4 (INTERNAL), each capable of supporting two INTERNAL and two EXTERNAL 5.25” Floppy's at 40 Track, 80 Track, Single
Density, Double Density, or Aerocomp FLIPPY Drives (Allowing Storage on the Back Side of TRS-80 Model 1 & 3 Drives) .
Image referenced above is from: http://pinouts.ru/Storage/5_12_floppy_pinout.shtml
NOTES:
Some Drives use External Terminator Resistors to PULLUP the signals to the + Power Supply Rail. If you are going to be installing (Model 1) drives that have the terminators installed, they must be removed for use with the Model 3 or Model 4 as the FDC already has the Pullup Resistors installed.
The 3.5" Standard IBM Style Floppy Drive uses Pin 2 - Reduced Write Current (/REDWC) from the controller to the drive to control the Density. The Model III & IV do not support this functionality, and the Drive's electronics are Pulled LOW via a 1K Resistor to Common (Pin 1) forcing LOW Density.
TRS-80 Model III Floppy Disk Controller Signals to Radio Shack Drives
19
20-->
21
22-->
23
24-->
25
26<--
27
28<--
29
30<--
31
32-->
33
34
9
10-->
11
12-->
13
14-->
15
16-->
17
18-->
Pin No.
1
2
3
4
5
6
7
8<--
Signal Name
Ground
N/C
Ground
N/C
Ground
N/C
Ground
/Index
Ground
/NDS1
Ground
/NDS2
Ground
N/C
Ground
/MOTEB
Ground
/DIR
Ground
/Step
Ground
/WDATA
Ground
/WGATE
Ground
/TRK00
Ground
/WPT
Ground
/RDATA
Ground
/SDSEL1
Ground
N/C
Pins 2, 4, 6, 14, 34 SPARE in J1 (EXTERNAL) & J4 (INTERNAL)
Description
--
Connector Clamp (Not used on TRS-80 Model III/IV Floppy Disk Controller FDC)
--
Reserved (Not used on TRS-80 Model III/IV Floppy Disk Controller FDC)
--
Reserved (Not used on TRS-80 Model III/IV Floppy Disk Controller FDC)
--
NINDEX/SECTOR (0=Index)
--
0=Drive Select 0 (Physical Drive 1 = Internal)
--
0=Drive Select 1 (Physical Drive 2 = Internal)
--
(Not used on Model III FDC)
--
0=Motor Enable Drive 1
--
0=Direction Select
--
0=Head Step
--
Write Data
--
Floppy Write Enable, 0=Write Gate
--
0=Track 00
--
0=Write Protect
--
Read Data
--
TRS-80 Model III & IV Floppy Disk Controller this is Side Select for the Read Head
--
Connector Clamp (Not used on TRS-80 Model III/IV)
TRS-80 Model IV Floppy Disk Controller Signals to Radio Shack Drives
13
14
15
16-->
17
18-->
19
20-->
21
22-->
Pin No.
1
2
3
4
5
6
7
8<--
9
10-->
11
12-->
23
24-->
25
26<--
27
28<--
29
30<--
31
32-->
33
34
Signal Name
Ground
N/C
Ground
N/C
Ground
N/C
Ground
/Index
Ground
/NDS1
Ground
/NDS2
Ground
N/C
Ground
/MOTEB
Ground
/DIR
Ground
/Step
Ground
/WDATA
Ground
/WGATE
Ground
/TRK00
Ground
/WPT
Ground
/RDATA
Ground
/SDSEL1
Ground
N/C
Description
--
Connector Clamp (Not used on TRS-80 Model IV Floppy Disk Controller FDC)
--
Reserved (Not used on TRS-80 Model IV Floppy Disk Controller FDC)
--
Reserved (Not used on TRS-80 Model IV Floppy Disk Controller FDC)
--
NINDEX/SECTOR (0=Index)
--
0=Drive Select 0 (Physical Drive 1 = Internal)
--
0=Drive Select 1 (Physical Drive 2 = Internal)
--
(Not used on TRS-80 Model IV Floppy Disk Controller)
--
0=Motor Enable Drive 1
--
0=Direction Select
--
0=Head Step
--
Write Data
--
Floppy Write Enable, 0=Write Gate
--
0=Track 00
--
0=Write Protect
--
Read Data
--
TRS-80 Model III & IV Floppy Disk Controller this is Side Select for the Read Head
--
Connector Clamp (Not used on TRS-80 Model III/IV)
Pins 2, 4, 6, 14, 34 SPARE in J1 (EXTERNAL) & J4 (INTERNAL)
3.5" Standard IBM Style Floppy Drive A Pin Out (On Twisted Cable - IBM Style Drives shipped Strapped for Drive 1)
20-->
21
22-->
23
24-->
25
26<--
27
28<--
29
30<--
31
32-->
33
34<--
10-->
11
12-->
13
14-->
15
16-->
17
18-->
19
Pin No.
1
2--->
3
4
5
6
7
8<---
9
/Step
Ground
/WDATE
Ground
/WGATE
Ground
/TRK00
Ground
/WPT
Ground
/RDATA
Ground
/SIDE1
Ground
/DSKCHG
Signal Name
Ground
/REDWC
Ground
N/C
Ground
N/C
Ground
/Index
Ground
/MOTEA
Ground
/DRVSB
Ground
/DRVSA
Ground
/MOTEB
Ground
/DIR
Ground
Description
--
Density Select 0=Low/1=High
--
Reserved
--
Reserved
--
0=Index
--
0=Motor Enable Drive 0
--
Drive Select 1
--
Drive Select 0
--
0=Motor Enable Drive 1
--
0=Direction Select
--
0=Head Step
--
Write Data
--
Floppy Write Enable, 0=Write Gate
--
0=Track 00
--
0=Write Protect
--
Read Data
--
0=Head Select
--
1=Disk Change/0=Ready
Standard IBM Style Floppy Drive A/B Twist Pinout
--
Wire 1-9
Wire 10
Wire 11
Wire 12
Wire 13
Wire 14
Wire 15
Wire 16
Wire 17-34
Controller
1-9
10
11
12
13
14
15
16
17-34
Drive A
1-9
16
15
14
13
12
11
10
17-34
Drive B
1-9
10
11
12
13
14
15
16
17-34
Description
No Change
Motor Enable Drive 0/1
Ground, No Change
Drive Select 0/1
Ground, No Change
Drive Select 0/1
Ground, No Change
Motor Enable Drive 0/1
No Change
So, the conductors 10 through 16 are twisted for IBM, but what you don't know is that pin 10, AND Pin 16 are ASSERTED
(HIGH) for the Motor ON signal. Your older computer doesn't follow this IBM standard, so we need to do one small modification to make the signals proper for older computers.
Instead of twisting conductors 10 thru 16, just cut off the last connector and now twist just conductors 10 thru 12. Now replace the connector accordingly. This keeps conductor 16 MOTOR ON for ALL Drives in the proper position. (Only Drives 0 & 1 can now be used......but if you route the conductor from Pin 10 to 14 (for D2) or Pin 6 (for D3) those drives can also be used, assuming your
Drive has the appropriate jumpers that can route the Drives Electronics to the proper pin on the connector.) I hope this is clear enough text to not be confusing. Maybe reading it a couple of times will help it sink in. There is a chart below showing the same information.
ACTUAL WIRING CONVENTION THAT IBM USES by also duplicating the Signal on Pin 10 that Pin 16 has using a Twist Cable.
6-->
8<---
/DRVSD
/Index
Drive Select 3 **
0=Index
10-->
12-->
14-->
16-->
/DRVSA
/DRVSB
/DRVSC
/MOTEA & B
Drive Select 0 ***
Drive Select 1 ***
Drive Select 2 **
0=Motor Enable for All Drives
NOTES:
** - Some Model Drives (TEAC FD-235HF) Have jumper positions for Drives 2 & 3 along with 0 & 1.
*** - Drive Select Wiring will be determined from the Actual Drive and if it has jumpers or not. If no jumpers are on the Drive, then it's Default is to be Strapped for Drive 1. Otherwise wire the Proper Drive Select from the Controller to the associated Pin shown for the Drive, and set the Jumper for that Drive.
DRIVE PIN
0 10
DRIVE STRAPPED FOR
D0
1
2
3
12
14
06
D1 DEFAULT (Jumper - connects the (D1) Pin 12 or (D0) Pin 10 Signals to the Drives Electronics)
D2
D3
TRS-80 FDC Controller
Sig Name
Connector Clamp * #
Spare *
Spare *
Index **
Select 0
Select 1
Spare *
Motor Enable
Direction
Step
Write Data
Write Gate
Track 00 **
Write Protect **
Read Data **
Side Select
Connector Clamp * ##
TYPICAL INTERCONNECT WIRING
PC-AT Style Controller
3.5" disk drive
Based on TEAC FD235HF
Sig Sig. Name Sig Name Sig Ground
02 0=Double/1=High Density ----->>-------------- REDWC 02 01
04 N/C ->>-
06 Drive Select D -------------------->>-------------- Drive Select 3
08 Index --------------------------------<<-------------- Index
10 Drive Select A -------------------->>-------------- Drive Select 0
04
06
08
10
03
05
07
09
12 Drive Select B -------------------->>-------------- Drive Select 1
14 Drive Select C -------------------->>-------------- Drive Select 2
16 Motor Enable A&B --------------->>--------------Motor Enable
12
14
16
18 Direction Select ------------------>>-------------- Direction Select 18
20 Head Step ------------------------->>-------------- Head Step
22 Write Data ------------------------->>-------------- Write Data
24 Write Gate ------------------------->>------------- Write Gate
26 Track 00 ----------------------------<<------------- Track 00
28 Write Protect ----------------------<<------------- Write Protect
30 Read Data -------------------------<<------------- Read Data
32 Side Select ------------------------>>------------- Side Select
34 Disk Change/Ready -------------<<------------- DC/Ready
20
22
24
26
28
30
32
34
11
13
15
17
19
21
23
25
27
29
31
33
Notes:
Signals denoted in BLUE need to be modified for Drive 0 & Drive 1 (Internal & External)
* - This Signal is not used on the Model III & IV
** - These Signals have Pullup Resistors Installed on the FDC for Internal and External Connectors,
so drives that have Terminator resistors installed need them removed.
# - This Signal needs to be Pulled LOW through a 1K Resistor for Double Density (2D) versus High Density (HD).
## - This Signal doesn't need to be connected since it isn't used.
This Chart depicts what needs to be done to interconnect all the signals properly, but gets confusing about exactly what is required. So, I've drawn out each interconnecting cable showing the exact wiring for each drive.
Floppy Disk Controller Pin Out for TRS-80 Model III & IV Drive 0 INTERNAL or EXTERNAL
TRS-80 Signals
Pin No.
8<--
10-->
12-->
14
16-->
18-->
20-->
22-->
24-->
26<--
28<--
30<--
32-->
Signal Name
/Index
/NDS1
/NDS2
N/C
/MOTEB
/DIR
/Step
/WDATA
/WGATE
/TRK00
/WPT
/RDATA
/SDSEL1
Description
X 1K Resistor to Common
NINDEX/SECTOR (0=Index)
Pin No.
2-->
4
6
--------------- 8<--
0=Drive Select 0
0=Drive Select 1
Not used on TRS-80 Model IV FDC
0=Motor Enable Drive 1
0=Direction Select
--------|
X | ----
X
10-->
12-->
14-->
--------------- 16-->
--------------- 18-->
0=Head Step
Write Data
Floppy Write Enable, 0=Write Gate
0=Track 00
0=Write Protect
Read Data
Side Select for the Read Head
--------------- 20-->
--------------- 22-->
--------------- 24-->
--------------- 26<--
--------------- 28<--
--------------- 30<--
-------------- 32-->
X 34-->
Pins 2, 4, 6, 14, 34 SPARE in J1 (EXTERNAL) & J4 (INTERNAL)
X represents Circuit Trace Cut
IBM Style Drive Signals
Signal Name
/REDWC
Description
Density Select 0=Low/1=High
N/C
/DRVSD
/Index
/DRVSA
/DRVSB
/DRVSC
/MOTEA & B
/DIR
Reserved
Drive Select 3
0=Index
Drive Select 0
Drive Select 1
Drive Select 2
0=Motor Enable Drives
0=Direction Select
/Step
/WDATE
/WGATE
/TRK00
/WPT
/RDATA
/SIDE1
/DSKCHG
0=Head Step
Write Data
Floppy Write Enable, 0=Write Gate
0=Track 00
0=Write Protect
Read Data
0=Head Select
1=Disk Change/0=Ready
Floppy Disk Controller Pin Out for TRS-80 Model III & IV Drive 1 INTERNAL or EXTERNAL
TRS-80 Signals
Pin No.
8<--
10-->
12-->
14
16-->
18-->
20-->
22-->
24-->
26<--
28<--
30<--
32-->
Signal Name
/Index
/NDS1
/NDS2
N/C
/MOTE A &
/DIR
/Step
/WDATA
/WGATE
/TRK00
/WPT
/RDATA
/SDSEL1
Description
X 1K Resistor to Common
NINDEX/SECTOR (0=Index)
0=Drive Select 0
Pin No.
2-->
4
6
--------------- 8<--
X 10-->
0=Drive Select 1
Not used on TRS-80 Model IV FDC
0=Motor Enable Drive
0=Direction Select
0=Head Step
Write Data
--------------- 12-->
14-->
--------------- 16-->
--------------- 18-->
--------------- 20-->
--------------- 22-->
Floppy Write Enable, 0=Write Gate
0=Track 00
0=Write Protect
Read Data
Side Select for the Read Head
--------------- 24-->
--------------- 26<--
--------------- 28<--
--------------- 30<--
--------------- 32-->
X 34-->
Pins 2, 4, 6, 14, 34 SPARE in J1 (EXTERNAL) & J4 (INTERNAL)
X represents Circuit Trace Cut
IBM Style Drive Signals
Signal Name
/REDWC
N/C
Description
Density Select 0=Low/1=High
Reserved
/DRVSD
/Index
/DRVSA
/DRVSB
/DRVSC
/MOTEA & B
Drive Select 3
0=Index
Drive Select 0
Drive Select 1
Drive Select 2
0=Motor Enable Drives
/DIR
/Step
/WDATE
/WGATE
/TRK00
/WPT
/RDATA
/SIDE1
/DSKCHG
0=Direction Select
0=Head Step
Write Data
Floppy Write Enable, 0=Write Gate
0=Track 00
0=Write Protect
Read Data
0=Head Select
1=Disk Change/0=Ready
REF: http://pinouts.ru/pin_Storage.shtml http://pinouts.ru/Storage/InternalDisk_pinout.shtml http://pinouts.ru/Storage/5_12_floppy_pinout.shtml
At this point the FDC to Drive hardware wiring setup should be complete. The FDC Signals to the 3.5” Drive Connector are wired correctly, but some drives allow multiple jumper settings to route these signals to different pins or allow changing signal states. If the STANDARD jumper settings for an IBM Style drive are used, the 3.5” Drive should function properly. There is a possibility of using a 3.5” 720K Drive,
3.5” 1.44K Drive, 720K Diskettes, 1.44K Diskettes (with the Density Hole covered for LOW Density), 40 Track configuration settings, or
80 Track Configuration Settings. I used Montezuma Micro CP/M ver 2.31, and configured my EXTERNAL 3.5” Drive for 80 Tracks, 1 head, and Double Density in the CONFIG software. That gave me an 80 Track, SS, DD, 400K Formatted Floppy. (I left the Drive size at 5.25” since a 3.5” drive selection isn't available and a 3.5” drive will function properly when connected.)
I have tested my wiring on three different drives. TEAC FD 235HF-117-U 720K Drive with a 720K Floppy, TEAC FD-235HF-B291-U5
Drive with a 720K Floppy, and a NEC FD1231H 1.44 Drive with a HD floppy with the Density Hole Covered to make a 720K Floppy.
I also used Montezuma Micro CP/M ver 2.31, and configured my EXTERNAL 3.5” Drives for 80 Tracks, 2 heads, and Double Density in the CONFIG software. That gave me an 80 Track, DS, DD, 710K Formatted Floppy. (I left the Drive size at 5.25” since a 3.5” drive
selection isn't available and a 3.5” drive will function properly when connected.) PIP does copy the files from A: to C: or D: properly.
Using NEWDOS-80 (Model 3 version) on my Model 4, I have set the PDRIVE according to the chart below and everything works accordingly.
Drive
Type
Drive
Size Density Sides SPT TI GRANS GPL
TD=A 5
TD=B 8
TD=C 5
TD=D 8
TD=E 5
TD=F 8
TD=G 5
TD=H 8
Single 10
Single Single 17
Single Double 20
Single
Double
Double
Single
Double
Single
Single
34
18
26
Double Double 36
Double Double 52
A 77
A or D 157
A 141
A or D 285
A 157
A or D 317
A 285
A or D 573
TD = Type Drive
TI = Type Interface (Standard or Apparat Disk Controller)
SPT = Sectors per Track
GPL = Grans per Lump
GRANS = Storage size on the formatted Floppy Disk
2
2
2
2
2
2
8
8
Pdrive,0 ….............Shows the Disk Parameters for the 10 drives stored in Memory.
Usage:
PDRIVE,SOURCE,DESTINATION,OPTIONS,,OPTIONS,OPTIONS,......,A
You can change a drives parameters, and read a new disk without a reboot. Use the following command ,A appended at the end:
PDRIVE,0,3,SPT=20,TC=40,A
PDRIVE,0,3=1,A
PDRIVE,0,3,TD=A,SPT=10,TC=40,A
PDRIVE,0,3,TD=G,SPT=36,TC=80,A
(If you don't add the ,A you will need to reboot after changing the PDRIVE Parameters.) PDRIVE Parameters are stored in RAM and will be RESET in the system on a reboot.
AMPRO Little Board Z80 CP/M Computer
The Ampro Little Board Computer supports four Drives. If you are using Drives such as the Tandon 100-2 with the Ampro, the manual states that the Terminator resistor (RP1 in Socket 2F) needs to be REMOVED in all Drives except for the last Drive on the Floppy Cable.
I am including a Photo of what Signals are associated with these PULLUP Resistors. Drive Pins 2, 4, 16, 18, 20, 22, 24 and 32 are
PULLED HIGH through a 150 OHM DIP Resistor. So, you should also be able to use a 3.5” Floppy Drive with the Ampro Computer.
I now have two TEAC FD-235 HF Drives connected to my Ampro Little Board Z80 Computer working correctly.
ENJOY!
Larry Kraemer 09-08-2010
10-18-2010
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