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Fixing Communication Errors in PC Access for Windows

Quick Contents

Related Documents
Talking to the MLS
Communication Errors
Fixing Communication Errors

Talking to the MLS

While you are online with your MLS, your computer "talks" to the MLS computer. That means the two computers send information to each other over a communication channel (usually a dial-up modem connection). Just as in human conversation, successful communication requires one party to be listening while the other is speaking.

Generally the MLS computer has no trouble "listening" when PC Access sends information to it. That's because most of the information PC Access sends to the MLS consists of characters you type at the keyboard, or short strings of characters you generate by clicking on command words in the PC Access Terminal window with your mouse. Humans do not type very fast compared to the speeds computers can handle. If you type something when the MLS is not ready to accept information, you can usually try again later with no problem.

Communication Errors

Things are different when the MLS sends information to your computer. The MLS can send lots of information very quickly, and some of this information makes your computer work very hard. The MLS may tell PC Access to update your display with text and photos. At the same time the MLS may tell PC Access to print a report, while continuing to send new information at high speed. If your computer becomes too busy obeying commands from the MLS to keep up with new information pouring in, you will get a communication error. When this happens, PC Access will inform you in the following ways:

In version 4.00 of PC Access for Windows and Builds earlier than Build 94, the word "ERROR" usually appears in the lower right corner of the Terminal window.
In Build 95 of version 4.00 of PC Access for Windows, the phrase "***COMMUNICATION ERROR*** Click Here for Help" usually appears in the lower right corner of the Terminal window.

Sometimes a communication error will cause PC Access to generate a General Protection Fault or even lock up your computer. If you get a GP Fault or lockup while online with your MLS, the Terminal window will not necessarily display the "ERROR" indicator even if a communication error caused the problem. However, if PC Access is prone to communication errors on your computer and it GP Faults or locks up occasionally, you will probably see the "ERROR" indicator at other times.

Therefore you should not ignore the "ERROR" indicator, even if PC Access appears to run normally for the time being.

When the "ERROR" indicator appears, you can identify the error type by selecting the Support | Comm Errors... menu item on the Terminal window. The Communication Errors window then displays the number of errors of four possible types PC Access has detected since you began your current online session. After you close the Communication Errors window by clicking the OK button, PC Access resets all the error counters to zero and clears the "ERROR" indicator.

The most common error is a Lost Data Error. (Your support representative may refer to this as the synonymous expression dropped characters.) This means your computer was unable to read a character arriving at your computer's serial port before new characters arrived and displaced it. Evidently your computer is sometimes too busy doing other things to keep up with incoming data.

Fixing Communication Errors

Several solutions are possible. You may need to try a combination of methods in the following list:

You can reduce the rate at which the MLS sends information.
You can enable your serial port to buffer a larger number of incoming characters, giving your computer more time to read them before newly arriving characters displace them.
You can change your computer's setup so it doesn't have to work as hard to keep up with information arriving from the MLS. You can also tell your computer to allocate more of its power to handle the incoming data.
You can upgrade your computer's hardware or system software.

Try these methods until you find the most attractive (or tolerable) combination that eliminates your communication errors. You can change settings on your computer without having to buy anything, so the first three categories above have no up-front monetary cost. Therefore you should try them first, and consider upgrading your hardware or system software only as a last resort. Be aware that some settings affect how PC Access runs on your computer and what features you will have available. In each of the following methods, we list the drawbacks (if any) of applying it.

If none of the following methods improve your problem, see Why am I getting Overruns? in The Navas 28800 Modem FAQ. This document is available on the World Wide Web at: http://modemfaq.home.att.net/

Reducing the rate at which the MLS sends information

On the PC Access for Windows Main Menu window, click the Setup Menu button.
On the Setup Assistant window, click the Advanced button.
- This is how you open the Advanced Setup Menu window. Remember this; you'll need to know how to get here for several other methods later in this document.
On the Advanced Setup Menu window, click the MLS Setup button.
On the MLS Setup window, try reducing the Speed setting. Click the OK button to close the MLS Setup window.

Drawback of this method: your online sessions run slower. You should use a lower modem speed while you try the following procedures. Once you find the combination of settings that lets you communicate reliably with your MLS, you can try increasing your speed again.

Enabling your serial port to buffer a larger number of characters

Your modem communicates with your computer via a serial port. If your modem is an external modem, you connect it to one of your computer's serial ports with a modem cable. If your modem is an internal modem, it contains its own built-in serial port (or an emulated serial port).

Every serial port contains a UART chip. UARTs come in two varieties: the 8250 and the 16550.

The 8250 UART is the low-speed design. It can store only one character arriving from your modem. If your computer does not read this character before the next character arrives, the character disappears and you get a Lost Data Error.

The 16550 UART is the higher-speed design. It stores up to 16 incoming characters at a time. This should suffice for reliable modem communication at speeds of 14,400 BPS and higher. (However, many things can go wrong with serial communication under Windows, so even a 16550 UART may not prevent Lost Data Errors on every computer.)

You can tell what kind of UART chips your serial ports have by running MSD. (See the topic Checking Your COM Ports with MSD in the PC Access for Windows Reference Guide or PC Access Help. If you have Windows 95, you may not have MSD.)

For PC Access to work best at high modem speeds, your modem's serial port must have a 16550 UART chip. If you don't have 16550 UART chip, you should upgrade your serial port.

Merely having a 16550 UART does not guarantee that Windows will run it in high-speed mode. You may need to tell Windows to do this, and how you do that depends on the version of Windows you are running. Follow the instructions below for your version of Windows:

Enabling your 16550 UART under Windows 3.1x

On the Advanced Setup Menu window, click the Modem Setup button.

On the Modem Setup window, look for some text in square brackets. This text should contain the phrase: fifo=1 or fifo=default . (If you don't see any text in square brackets, you should update your copy of PC Access.) If it says fifo=0, Windows is running your UART in 8250 mode. If it says fifo=0 and you actually have a 16550 UART, you need to enable the high-speed mode by completing these steps:
- Make a backup copy of your SYSTEM.INI file on a spare diskette (do not use any disks you received with software you have purchased). This file will probably be in your C:\WINDOWS directory.
  - Put your backup diskette in a safe place. Normally you will not need it, but if you damage your SYSTEM.INI file from improper editing, you will need to restore the copy on your hard drive from your backup copy.
- Open your SYSTEM.INI file in Notepad.
- Find the [386Enh] section.
- Add a line to this section like the following:
  - COMnFIFO=1
  where n is the number of the serial port your modem uses; for example, type: COM2FIFO=1 if your modem uses COM2.
- If you already have a line like: COMnFIFO=TRUE, change it. Only COMnFIFO=1 will enable your 16550 UART's high-speed mode.
- If you have any doubts about your ability to edit your SYSTEM.INI, have a competent technician perform the above procedure on your computer.
See below for other settings you can change in Windows 3.1 that may let your computer communicate better.

Enabling your 16550 UART under Windows 95, 98, NT

Click Start | Settings | Control Panel.
In the Control Panel folder, double-click the System icon.
On the System Properties dialog, click the Device Manager tab.
Open the Ports branch by double-clicking on it.
Highlight the Communications Port your modem uses, and click the Properties button.
On the Communications Port Properties dialog, click the Port Settings tab. Click the Advanced button.
On the Advanced Port Settings dialog:
- Check the Use FIFO buffers box.
- The default setting for Receive Buffer is 14 bytes. You may have fewer comm errors if you reduce this to a lower value. For a technical discussion of this setting, see Why am I getting CRC errors (overruns)?, scroll to item (21), in The Navas 28800 Modem FAQ.

Changing your computer's setup

You can change your computer's setup to help it keep up with information arriving from the MLS.

Turn off View Photos During Download:

On the Advanced Setup Menu window, click the MLS Setup button.
On the MLS Setup window, click the More>> button. In the Settings group, un-check the View Photos During Download box. Click the OK button.

Cost of this method: PC Access will download an entire photo before displaying it. (You may decide this does not matter.)

Disable the scrollback:

On the Advanced Setup Menu window, click the Defaults button.
On the Defaults Setup window, check the Disable Scrollback box. Click the OK button.

Cost of this method: you won't be able to use the scrollback to review your online session. (Experience shows that very few agents are aware of the scrollback feature, so you probably won't miss it.)

Disable Comm Events:

If you are running a version of PC Access older than Build 93, you should download an update from the MFM web.
Once you are running Build 93 or later, on the Advanced Setup Menu window, click the Modem button.
On the Modem Setup window, click the More>> button.
Check the Disable Comm Events box. Click the OK button.

Cost of this method: your online sessions may become slightly "jerkier".

Enable Time Division Processing:

If you are running a version of PC Access older than Build 95, you should download an update from the MFM web.
Once you are running Build 95 or later, on the Advanced Setup Menu window, click the Modem button.
On the Modem Setup window, click the More>> button.
Make sure the Time Division Window field shows a value greater than zero. The default value is 55 milliseconds; this is a reasonable value. Click the OK button.
On the Advanced Setup Menu window, click the MLS Setup button.
On the MLS Setup window, click the More>> button. In the Flow Control group, select the Time Div./Hardwr. radio button. Click the OK button.

Cost of this method: your online sessions will run 10%-30% slower for a given Speed setting. However, this method is highly effective for eliminating otherwise intractable communication errors.

Set your job timeout to zero:

On the Advanced Setup Menu window, click the Printer(s) button.
On the Printer Setup window, highlight the printer you are using as your default printer in PC Access for Windows, and click the Edit button.
Type the value 0 in the Job Timeout field (the default is 2 seconds).
Additional SYSTEM.INI settings:
1. Be sure you are using the standard Windows serial communication driver. You should have the following line in the [boot] section of your SYSTEM.INI file:
  comm.drv=comm.drv
2. In Windows 3.1 and 3.11, you can add the following lines to the [386Enh] section in your SYSTEM.INI file:
  - COMBoostTime=10
  - COMnBuffer=1024
  where n is the number of the serial port your modem uses; for example, type: COM2Buffer=1024 if your modem uses COM2.
3. In Windows 3.11 for Workgroups only, you can add the following line to the [386Enh] section in your SYSTEM.INI file:
  - COMnRxTrigger=4
  where n is the number of the serial port your modem uses. Legal values for COMnRxTrigger are 14, 8, 4, and 1. Try reducing the value if you continue to get communication errors. Set the value to 1 only if you are desperate.
Set up a Permanent Swap File and Enable 32-bit disk access (Win3.1x and Windows 3.11 for Workgroups):
1. Open the Main group window in Program Manager.
2. Double-click the Control Panel icon.
3. In the Control Panel window, double-click the 386 Enhanced icon.
4. On the Enhanced dialog, click the Virtual Memory button.
5. On the Virtual Memory dialog, click the change>> button to view additional options. The options you see depend on what Windows thinks about the capabilities of your computer's hard drive subsystem.
6. If the Use 32-Bit Disk Access checkbox is visible, check it. If the Use 32-Bit File Access checkbox is visible, check it also.
7. In the New Swapfile Settings group, specify the following:
  - Select Permanent for the Type.
  - Select at least 20000 KB for the New Size if you have sufficient space on the Drive you have selected.
8. Click the OK buttons on the Virtual Memory and the Enhanced dialogs to accept your new settings.
Try changing your display driver to the Windows VGA.
- Occasionally an accelerated video card will have a driver that prevents the Windows communication driver from working correctly. If changing to the Windows VGA driver eliminates your communication errors, you should obtain an updated driver from your video card manufacturer.
  - Warning! Some video cards are not compatible with the standard Windows VGA driver. Before you try changing your video driver to Windows VGA, make a backup copy of your SYSTEM.INI and WIN.INI files on a spare diskette. If Windows will not restart after you change to VGA, you can copy your backup versions of SYSTEM.INI and WIN.INI from your MS-DOS prompt. If you have any doubts about your ability to do this, do not try changing the Windows display driver.
- If you are running Win3.1x or Windows 3.11 for Workgroups, you can change your display driver to Windows VGA as follows:
  1. Open the Main group window in Program Manager.
  2. Double-click the Windows Setup icon.
  3. On the Windows Setup window, select the Options | Change System Settings... menu item.
  4. On the Change System Settings dialog, pull down the Display list. Write down the complete name of your current display driver (so you can change it back later).
  5. Select VGA.
  6. Click the OK button. Windows will ask you if you want to restart Windows. Yes, you do.
- If you are running Windows 95, you can change your display driver to Windows VGA as follows:
  1. Click Start | Settings | Control Panel.
  2. Double-Click the Display icon.
  3. Click the Settings tab on the Display Properties dialog.
  4. Click the Change Display Type... button.
  5. Click the Change... button to the right of the Monitor Type field.
  6. On the Select Device dialog, highlight (Standard monitor types) in the Manufacturers list.
  7. On the Models list, highlight the Standard VGA entry. Click the OK button.
If you are running SMARTDRV.EXE, make sure to turn off write caching on all drives with the X command-line parameter.
If you are running Windows for Workgroups version 3.11, make sure you have disabled write caching for the 32-bit file system.
Try disabling Print Manager (Windows 3.1x). This may be helpful if your communication errors happen while you are printing reports from your MLS.
1. Open the Main group window in Program Manager.
2. Double-click the Control Panel icon.
3. On the Control Panel window, double-click the Printers icon.
4. On the Printers dialog, un-check the Use Printer Manager box.
5. Click the Close button.
Try disabling Print Spooling (Windows 95):
1. Click Start | Settings | Printers.
2. Find the printer you are using in PC Access for Windows. Right-click its icon and select the Properties item from the popup menu.
3. Click the Settings tab on the Display Properties dialog.
4. Click the Details tab on the Properties dialog for the printer. Click the Spool Settings button.
5. Select Print directly to the printer.
6. Click the OK buttons on the Spool Settings and Properties dialogs to accept your change.
Standard Port vs. ECP Port
Exit from other Windows applications. This may be helpful if your communication errors happen while you are printing reports from your MLS.
- In Windows 3.1x, press Ctrl-Esc to display the Task List. If possible, exit all other Windows applications so the only entries in the Task List are Program Manager and PC Access for Windows.

Upgrading your computer's hardware or system software

You can speed up your computer by upgrading its hardware.

Buy a serial port with a 16550 UART if you don't already have one.
Buy more RAM. If your computer has only 4 MB of RAM it may have to swap to disk frequently during complex operations such as printing. This can prevent your computer from keeping up with characters from the MLS. Even 8 MB may be insufficient if you print color photos, or black-and-white photos at high (600 DPI) resolution.
Buy a Hayes ESP communications accelerator. This is only useful if you have an external modem. The Hayes ESP card turns even the slowest, flakiest computer into a communication powerhouse.
- On the World Wide Web, you can read about the Hayes ESP on Hayes' home page at: http://www.hayes.com
Try a different modem. Occasionally a particular modem will not work correctly with a particular computer, even though the same modem might work fine in another computer. As a general guideline, external modems usually work better than internal modems, for reasons MFM does not understand. If you do decide to try another modem, try to borrow one for testing before you buy. Always insist on a money-back guarantee when you buy any modem.

You can sometimes improve serial communication on your computer by upgrading Windows. Windows for Workgroups 3.11 and Windows 95 both have superior support for serial communication than does Windows 3.1.