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SERIES II INTELLIGENT DATA/FAX MODEMS
3.2.2 The 16550 UART and Windows 3.1
Windows 3.1 may cause a loss of data when communicating at high speed, even with a 16550 UART installed. Because Windows is multitasking—it switches between several programs running at the same time— it can make the serial port wait briefly while Windows performs other tasks. Meanwhile, incoming data can be lost. The older 8250A and
16450 UARTs can store data in a one-byte first in-first out (FIFO) buffer
(a memory area in the UART in which the first bit in is the first out), but once the buffer is full, the data is lost. The 16550 has a 16-byte FIFO buffer, which accounts for much of its high speed. However, in Windows
3.1, the 16550’s FIFO buffer is disabled by default. To enable the buffer, use Notepad to open the SYSTEM.INI file in your Windows directory, and add the following line to the [386Enh] section:
COMnFIFO=1 where n is the number of the COM port the 16550 is installed on.
For example, if the 16550 is installed on COM2, the line should be:
COM2FIFO=1
After you save SYSTEM.INI you must restart Windows for the change to take effect.
However, there is another problem when the FIFO buffer is enabled:
Windows cannot recognize the COM port because of a bug in the
Windows 3.1 serial port driver, COMM.DRV. The only way around this problem is to replace the COMM.DRV file in the WINDOWS\SYSTEM directory with another driver. Several drivers are available commercially, on the World Wide Web, or on BBSes that will solve this problem.
A freeware driver called CyberCom is available as CYBERC.ZIP on
CompuServe in the IBM Communications Forum, Library 0. CyberCom will enable Windows communications at speeds up to 115,200 bps if you have a 16550 UART installed.
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Table of contents
- 8 Introduction
- 8 How To Use This Manual
- 11 What is in Your Modem Package?
- 11 Modem Features
- 12 Fax Features
- 13 Technical Specifications
- 17 Power
- 17 Modem LED Indicators
- 19 Controls on PC Board
- 20 Safety Warnings
- 21 Installation
- 24 Is Your Series II Modem Ready for Use?
- 25 Operating Your Series II Modem
- 26 Simple Operations
- 26 The Answer/Originate - Voice/Data Toggle Switch
- 27 Introduction
- 27 Serial Port Limitations
- 28 How Can You Identify Your UART Type?
- 29 The 16550 UART and Windows
- 30 Configuring Your Software
- 30 Configuring Software for Your Modem
- 31 PC Initialization Strings
- 31 Changing Default Parameters
- 32 Other Parameters
- 32 Macintosh Initialization
- 33 Configuring Software for Your Computer
- 33 Configuring Software for the Remote System
- 34 Terminal Emulation
- 34 File Transfer Protocols
- 34 When to Disable Data Compression
- 35 Disabling Error Correction
- 36 Introduction
- 36 Dialing/On-Line/Answering
- 38 Auto. Leased Line Restoral Operation (336+ Only)
- 38 Manual Dial Backup Call Termination (336+ Only)
- 38 Dial Backup and Leased Line Restoral (336+ Only)
- 40 Dial-Up Operation (336+ Only)
- 40 Manual Call Origination
- 41 Automatic Answering
- 42 Manual Answering
- 42 Handshaking Details
- 43 Call Termination
- 45 Introduction
- 45 AT Command Editing
- 46 Functional Modes
- 47 Summary of AT Commands
- 51 Result Codes
- 53 Dialing Commands
- 53 Dialing Action Commands
- 55 Dial Modifier Commands
- 59 Phone Number Memory Commands
- 61 Configuration and Default Storage Commands
- 64 Command Response (Result Code) Commands
- 67 Phone Line Conditioning Commands
- 69 RS232C Interface Control Commands
- 71 Error Correction Commands
- 76 Flow Control Commands
- 82 Pass-Through and Pacing Commands
- 83 Speed Conversion Commands
- 86 Immediate Action Commands
- 91 Line Probe Commands
- 93 Introduction
- 103 Reading and Assigning S-Register Values
- 103 Examples of Assigning Values
- 104 Examples of Reading Values
- 104 AT Command and S-Register Summary
- 105 Introduction
- 105 Callback Feature Description
- 106 Remote Configuration Description
- 106 Configuration
- 112 Remote Configuration Procedures
- 113 Commands
- 115 Remote Configuration/Callback Security S-Registers
- 117 Introduction
- 118 Local Analog Loopback Test/V.54 Loop
- 119 Digital Loopback Test/V.54 Loop 2 (Local/Manual)
- 121 Digital Loopback Test/V.54 Loop 2 (Remote/Auto.)
- 122 Back-to-Back Test
- 124 Synchronous Mode Testing
- 124 Local Analog Loopback Test (Synchronous Mode)
- 125 Digital Loopback Test (Local/Manual) (Sync Mode)
- 126 Digital Loopback Test (Remote/Auto.) (Sync Mode)
- 128 Introduction
- 129 DIP-Switch Option Settings
- 137 Speaker Volume Control
- 138 Recording Option Configurations
- 140 Possible Causes and Solutions
- 148 Contacting Black Box
- 148 Recording Modem Information
- 149 Making the Call
- 149 Shipping and Packaging
- 150 Upgrading the Series II Modem’s Firmware
- 151 Appendix B - Dial Pulse and Tone-Dial Frequencies
- 152 Appendix C - Command Summary
- 165 Appendix D - DIP-Switch Summary
- 168 Appendix E - S-Register Summary
- 172 Appendix F - Result Code Summary
- 175 Appendix G - V.25bis Operation
- 188 Appendix H - Series II Modem Cables
- 190 Appendix I - RS232C Interface Specifications
- 196 Appendix J - Regulatory Information