Can somebody tell me, without going deeply into pin outs, what the difference is between a null modem cable and a regular serial cable? I have 1 serial cable that says "Null Modem" on it, and another cable that does not. They both have 9 serial connectors one one end and 25 on the other. What are the uses for both? Can I use a null modem cable to hook up an external modem on a com port of a PC for instance? What about using a null modem cable to hook a printer up to a terminal? Is there any difference? Thanks alot!

A Null modem cable is used for connecting two computers together via the serial port. Does the same job as a Cat5 crossover cable soes for Ethernet. You need a straight through cable to connect a modem. You might also find the null modem cable has male sockets on both ends while the straight through cable has male and female sockets. If the null modem cable does not have male connectors you will need a gender changer to make it so. Stuart

A serial port can transmit and receive data. It has seperate pins to do this. If you connected two computers together using a regular serial cable you would connect the two transmits to each other. Also you would connect the two receives together. What you really want is to connect each transmit to the other computers recieve and the receive to the other computers transmit. The null modem cable does this for you. Some devices you connect to the serial port reverse the connections internally for you. This allows you to use a regular serial cable with them.

G'day, Just to expand on this a little bit- egkenny has most of it covered- you need to crossover all of the contol pins too (CTS, DTS etc..)for a full duplex system. But, the important thing to grasp is that the standard equipment for serial use is DTE (Data Terminal Equipment) and DCE (Data Communications Equipment). A standard serial cable connects a DTE to a DCE. A PC is a DTE, so a null modem cable is required to connect them (DTE to DTE). A modem is a DCE, so a standard serial cable is used. Those two will be the most frequent connection you will come into contact with. For anything else you will need to find out which one they are (not easy because manufacturers are a bit slack in this regard) Good luck, Elric