A Quick Tutorial-null Modem Cables

[carlos60]

A QUICK TUTORIAL-NULL MODEM CABLES

This is mainly geared round those having problems flashing the boxes or any other device which requires a null modem cable. Other digital or satellite boxes may require a different cable.
To flash some boxes you need a null modem cable. This is a type of rs232 serial cable, but not all rs232 cables are null modem cables. rs232 is a communications protocol which can use several cable wiring configurations.

This is the wiring arrangement in a null modem cable.

You can see that a lot of the pins do not connect straight through. You will not be able to see this on the cable itself because all the connections are encapsulated so you need to be sure that you buy the right cable from someone who knows what they are talking about! The important connections to successfully flash your boxes are

2-----------------------------------3
3-----------------------------------2
5-----------------------------------5

This is what both en#s of the cable should look like if its for a box(x) - it's a female end at both en#s - holes not pins.

Another type of rs232 cable is a "straight through" cable where each pin on the connector is connected "straight through" e.g. pin 2 connects to pin 2, 3 to 3 etc See the diagram below. A straight through cable WILL NOT WORK ON A SOME BOX - A STRAIGHT THROUGH serial cable looks exactly the same as a null modem cable from the outside but the wiring is completely different inside, like this

DTE ............................................... DSE
side ............................................... side
2 Transmitted data ----------------> Received data 2

3 Received data <---------------- Transmitted data 3

4 Request to Send ---------------> Clear to Send 4

5 Clear to Send <--------------- Request to Send 5


14 Sec.Transmitted data ----------------> Sec. Received data 14

16 Sec. Received data <---------------- Sec. Transmitted data 16

19 Sec. Request to Send ---------------> Sec. Clear to Send 19

13 Sec. Clear to Send <--------------- Sec. Request to Send 13

This is what the socket on your pc or laptop should look like - these are pins not holes!

if you are using a laptop you need to find a connector like the one marked 1 here - this is the serial connector.

NOTE: the connector marked 6 is a video out, not a serial connector.

If your pc hasn't got a serial connector you need one of these converters - shown below. You then plug one end of your null modem into the adapter and the other end into the box (or whatever).


You then use a USB connector like the one marked 5 on the laptop picture above.

Here the end of the lesson.