Parallel Cable; Using The Windows 3.1 Terminal Program; Hardware Hints - ZyXEL Communications 2864 Series User Manual

For high speed serial connections at 230.4Kbps or 460.8Kbps, use a low-capaci-
tance cable. Also, keep the cable as short as possible.

Parallel Cable

Use a 25-wire cable with a male connector at one end and a female connector at the
other end to connect the PC's parallel port to the modem's parallel port. Keep this
cable as short as possible. This cable may also be used to make the 25-pin serial con-
nection.

Using the Windows 3.1 Terminal Program

You will not be able to use a transfer rate of more than 19.2Kbps with this pro-
gram. With a special comm driver, you may be able to run the serial port at a higher
speed. Please consider this when you set up your modem's DTE to DCE speed. If
you are using a ZyXEL 2864 modem's parallel port for PC-modem communica-
tion, setting the DTE speed has no actual physical meaning. The actual speed de-
pends on how fast and efficient the Windows program can run. The parallel
connection guarantees no data loss, no matter how fast or slow the Windows pro-
gram runs. Fast 286, 386, 486 and Pentium PCs allow you to lock the serial port at
speeds above 38.4Kbps. Check whether your PC and software allow this. Refer to
the ZyXEL Serial/Parallel I/O Adapter Card section in this chapter for information
about high-speed connections.

Hardware Hints

The serial port is driven by interrupts. Every interrupt needs a certain amount of
overhead processing time. Too many interrupts reduce the computer's efficiency.
The UART 16450 is very commonly used in serial port devices. For every character
(byte) received, it generates an interrupt. If your hardware allows it and if your soft-
ware supports it, replace the 16450 UART with a 16550 model. This newer chip
has an internal buffer and generates an interrupt for up to every 16 characters (sev-
eral trigger levels are available). With this UART installed, you may drive your serial
port at 57600 bps and above. Among other programs, the shareware terminal pro-
gram Terminate allows you to determine which type of UART(s) is/are installed in
your system without opening the computer.
If you run Windows, OS/2 or another multi-tasking operating system, you should
set your serial port speed to 38400 bps or less. In these environments, the serial port
is usually served slower than in a single task environment.
Another option in multi-tasking environments is to increase the priority of your se-
rial port. If you use Windows, read the file SYSINI.WRI. This file is placed into the
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