PC Access for Windows Reference Guide

for PC Access for Windows 4.30.158

Unreliable Communication

Symptoms include occasional garbage characters, dropped characters, carrier loss, and program lockups. (If you get garbage characters as soon as your modem connects to the MLS, see Terminal window displays gibberish.) These can result from several possible causes, including the following:

· You have a high-speed modem and an 8250 UART on the serial port your modem uses. A high-speed modem requires a 16550 UART for best results. You may get away with an 8250 UART if your computer is very fast, but why take risks? Run MSD to see what kind of UART you have.

¨ Check your COMnFIFO setting in your SYSTEM.INI file to insure that Windows is running your 16550 UART at full speed.

· You are running SMARTDRV with write-caching enabled on your hard disk. Be sure you have disabled write caching on SMARTDRV if you are running it. In the Windows Control Panel, set your permanent swap file size to at least 8MB. Enable 32 bit Disk Access if it is available. Enable 32 bit File Access (available in Windows for Workgroups only). (When you use 32 bit File Access, Windows automatically disables SMARTDRV.)

· You haven't enabled hardware flow control, and your MLS requires it.

· Another program conflicts with PC Access. For example, you usually can't run another communication program or a FAX program while you run PC Access for Windows. Close all your other Windows applications and call your MLS again from PC Access. (To find out what other Windows applications you are running, press Alt-Tab repeatedly. This cycles you through a list of all Windows applications currently running on your computer.)

· You are running the POWER.EXE device driver. This caused problems for some PC Access for DOS users. MFM does not know yet whether it will cause problems for PC Access for Windows.

· Your telephone line polarity may be reversed. Check it with a tester available from your neighborhood telephone store. You may also have a faulty telephone cable. If you have an external modem, your serial cable may be bad, or the connection may be loose.

· Some inexpensive modems do not provide hardware error correction. Often the only way to find this out is to call the manufacturer of your modem and ask. If your MLS is a Maestro System or Master System, you may have to upgrade your modem to a model which provides true hardware error correction. If you can exchange your present modem, the cost of upgrading is usually low (ca. $20).

¨ If your modem documentation says your modem uses the Rockwell Protocol Interface (RPI), then your modem almost certainly will not work with an MLS, unless you obtain and install the Windows RPI driver from Rockwell. Most RPI modems are older, slower models and have compatibility problems with many other kinds of software. If you buy a new modem you are unlikely to get stuck with an RPI modem.

· If you are using your computer's built-in speaker to play .WAV files (Windows sounds), your sound driver will interfere with communication programs such as PC Access. The best solution is to disable your sound driver while running PC Access, or upgrade to a sound card.

· Some computers are unable to receive characters from a modem while simultaneously writing to disk. On such a computer you should try disabling the scroll back on the Defaults Setup window.

· If you only have communication problems while you print a host report, see Dropped Characters while Printing Host Reports.

This topic has changed for PC Access 4.30 (Monday, March 27, 2000).

Last modification date: Friday, January 17, 2003 00:58:56