ComRing
version 1.17
packet driver for "network" based on serial ports
Copyright ©1997,8 by Jan Bobrowski
This is free software. Use it at your own risk.
Distribution unlimited.

MOTIVATION
  The intention of ComRing is to connect more than two computers through ordinary serial ports. ComRing cable allows you to build "network" based on serial ports using one port per computer. It is slow but cheap.

ComRing software also offers network interface for traditional Null-modem. It may be useful for games that don't handle it properly.

HARDWARE
 
Serial port was developed for computer-modem connection. It is widely used to connect two computers using null-modem cable. It consists of two units: trasmitter and receiver. They may be connected to different computers (?). The basic idea of ComRing is to organize computers in logical form of ring. Data will flow in fixed direction. 


 A -----> B  
 ^        |
 |        |
 |        v
 D <----- C
You should prepare 3-wire ComRing cable:

lineDB9DB25
TxD32 transmit connected to RxD of next computer
RxD23 receive connected to TxD of previous computer
GND57 ground common for all computers 


    DB25                                   DB9
     _____________________________          _____________
   1 \ . T R . . . G . . . . . . / 13     1 \ . R T . G / 5
   14 \ . . . . . . . . . . . . / 25       6 \ . . . . / 9
        -----------------------                -------
Cable for three computers: 


        Computer A      Computer B      Computer C

           TxD ----------- RxD
                           TxD ----------- RxD
           RxD --------------------------- TxD
           GND ----------- GND ----------- GND
Cable for four computers: 


 Computer A      Computer B      Computer D      Computer C

    TxD ----------- RxD
                    TxD --------------------------- RxD
                                    RxD ----------- TxD
    RxD --------------------------- TxD
    GND ----------- GND ----------- GND ----------- GND
You can use Null-modem cable as two-node ComRing.


SOFTWARE
  ComRing cable for more than two computers will not work with an ordinary SLIP or PPP packet driver. You can't use it as null-modem. I wrote special packet driver (comring.com) to make it usable. It is class 1 driver - it emulates DIX ethernet (specification 1.11, basic and high-performance functions). You must install it on each computer to close circuit.

To distinguish between different computers in the "network" specify a single letter, identifying your computer. It is the first parameter (and only required) to the packet driver. When you invoke comring a on one computer you can't use a (or A) on others. This letter is used to generate ethernet address.

Syntax is: comring id [parameter]...

You may use following parameters:

com# com port (default: 2)
baud=# baud rate (default: 115200, it may be slowed down)
nodes=# maximal number of computers connected (default: 3)
int=# interrupt for packet driver (hex, default: 60)

If you're using nonstandard port you should specify:

port=# port address
irq=# irq number

Example: comring A baud=9600 com1

Note: Comring is supposed to be a DOS program. It can interfere with Windows, however probably it will work in DOS box.

GAMES
  Most games don't use packet driver interface. They expect IPX network. You may use Intel's pdipx adapter included in this package. It has been configured for DIX ethernet (command: econfig.exe pdipx.com shell:e 8137).

Invoking commands may look like:

comring B com1 baud=57600
pdipx
game
You should remember: if one computer will not work correctly, the whole network won't work.

Please send me success/failure reports. (jb@wizard.ae.krakow.pl)