Null modem cables connect two serial devices that require a null modem configuration; This product is covered by a Lifetime Limited Warranty (coverage details) View Full Product Details. Tripp Lite Part Number P450-010. Add to List Toggle Dropdown. A: A standard 'null-modem serial cable' (optionally attached to the PC via a USB serial interface), or a Bluetooth serial adapter. The null-modem cable needs to be wired for 'full handshaking' (not 'loopback handshaking' or 'partial handshaking'). These cables are architecture-neutral, i.e. They are the same for PC, Amiga and other systems. Null modem is a communication method to directly connect two DTEs (computer, terminal, printer, etc.) using an RS-232 serial cable.The name stems from the historical use of RS-232 cables to connect two teleprinter devices or two modems in order to communicate with one another; null modem communication refers to using a crossed-over RS-232 cable to connect the teleprinters directly to one. Null modem, also called crossover, is a term associated with serial (RS-232) cables. A standard serial cable, also called an AT cable, has the wires inside the cable running straight through. Take a DB9 cable as an example. Pin 1 on one end of the cable would be connected to Pin 1 on the other end. Null Modem Cable Serial RS232 9 Pin DB9 Male to DB9 Female Gender Changer Lead. 1m 9 Pin DB9 Serial RS232 NULL Modem High Speed Shielded Cable 008437 £2.68. PC Serial Data Transfer (Null Modem) Lead / Cable, 9-way DB9 Female - Female, 5M.
While working on the next update to ACOM Director Plus (yes, work is now continuing on it), I couldn’t figure out why my code to turn on the ACOM600S was not working. I’d previously put this down to the fact that I have an early model and perhaps this wasn’t implemented then. I resorted to using my scope to check that the DTR and RTS lines were in fact being activated properly which is when I discovered that my Null Modem cable i’d been using for years now is not in fact a proper Null Modem Cable.
A normal (proper) Null Modem cable has the following wiring, notice the crossover of the DTR & DSR pins and the RTS & CTS pins, these are used for the remote power on of the ACOM600S, ACOM1200S and ACOM2000A with the RPON Module.
However after checking the wiring on my (commercially purchased) Null Modem Cable, I found it is actually wired like this.
As pins 2 & 3 are crossed, it still works fine for normal serial communications (without handshaking obviously) however all other pins are straight through, so anything relying on the proper use of handshake signals will fail.
Rs232 Cable Pinout
The moral of the story, if you have issues with remote power on of the ACOM600S, ACOM1200S or ACOM2000A (or anything else that makes use of any control pins), make sure your Null Modem cable is actually wired fully to the Null Modem standard and not a half baked cable like mine.
Null Modem Cable Rs232
The #1 loading problem is communication between PC and IRD. This is usually a serial and null modem cable problem.
Null Modem cables look like straight serial cables and the only way you can tell the difference by looking is most Null Modem cables are marked with 'NM' or 'Null Modem'.
Some dealers are shipping Pansats with straight modem cables and NOT Null Modem.
If your cable is not marked, the only way you can tell them apart is with a multimeter or continuity tester. With a straight thru serial cable, pin 2 should lead to pin 2 and pin 3 should lead to pin 3.
A null modem cable pin 2 should lead to pin 3 and pin 3 should lead to pin 2.
If straight thru then all pins should point to the same number on the other end.
Your local rat shack has the replacement adapter for under $10.00 , Part # 26-0264 ~ female DB9 to male DB9 ~ pins 5 straight & 2 & 3 crossed ..
Want to know what cable you need to flash that shiny,new receiver ? There are two types of cables used, and both look the same on the outside, but are wired differently internally. They are the straight DB9 RS232 female to female cable, and the Null 9 pin RS232 female to female cable. The straight DB9 cable has all pins connected the same at both ends(pin 1-1, 2-2,3-3,etc.). The Null cable(also known as a Null-Modem) has pins 2 and 3 crossed(pin 2-3, 3-2). You can use a straight DB9 cable to program receivers requiring a Null cable, by purchasing an inexpensive Null adapter to attach to one end of the straight DB9 cable. This allows one cable to be used for any receiver.
Hope this helps.