1990 Ken Schmitz Milwaukee, Wisconsin
The following is a description and diagram of a typical Null Modem Adaptor.
This adaptor is used when hooking two computers together using the 25 pin connectors on the RS232 serial ports. I made this adaptor for use with the software "Fast Wire II" but can be used for any other communication applications. Utilizing a one-for-one 25 conductor cable and the adaptor on one end, I was able to use the software and transfer files at an incredible 115300 baud allowing a 360K file to be transfered in 30 to 40 seconds. Extra time is needed for smaller separate files but it is still very fast. The software is especially handy when transfering from 3.5" to 5.25" disks and visa versa or for big files from hard disk to hard disk. (Yes, I like it!)
I made this document to help those who need to know how to make there own standard store bought Null Modem Adaptor. The connector part numbers are DB 25P (male) for the left side and DB 25S (female) for the right side of this drawing.
GND 1 >--------------------------< 1 GND
TX 2 >--------------------------< 3 RX
RX 3 >--------------------------< 2 TX
RTS 4 >---|----------------------< 8 CD
|
CTS 5 >---| |---< 4 RTS
|
CD 8 >----------------------|---< 5 CTS
GND 7 >--------------------------< 7 GND
DSR 6 >--------------------------< 20 DTR
DTR 20 >--------------------------< 6 DSR
The following describes the names for each signal:
TX = Transmit Data
RX = Receive Data
RTS = Request to Send
CTS = Clear to Send
CD = Carrier Detect
GND = Logic Ground
DSR = Data Set Ready
DTR = Data Terminal Ready