Near Intersection of I-35 & I-90 Southern Mn. | In the old days when teletype machines were used to transmit information they were normally hooked up over a phone line and used a modem device. Some of these modem devices were designed so that a regular telephone handset was pushed into the modem enclosure.
If you had a teletype in one place and connected it to a modem it could communicate with another teletype at another location which was also connected to a modem.
If two teletype machines were right beside each other and it was desirable to hook them together without a phone connection, the Tx and Rx (as well as some other wires needed) to be reversed. Then the Tx line from Machine A went to the Rx line of Machine B etc.
Since there was no modem involved in this setup, the wiring cable that did the crisscrossing came to be known as a Null Modem since you were NOT using a MODEM. |
Still problems 2577
