Hi everyone

Does anyone know where I can get hold of a null modem cable in Chiang Mai? The vendors I have asked so far around the Computer Plaza area only understand 'Serial' (as in 'cable'), but I think that the null-modem cable isn't the same as an ordinary serial cable.

Any advice would be much appreciated.

H.

Ask them to make you one. Just tell them that in lieu of flipping the Tx and Rx lines, to keep them straight thru.

Concerning a null-modem CAT-5 cable, I was able to buy one of these at Pantip (in Bkk). So I know they are available. If you are looking for a null-modem serial cable (RS-232), then these are a breeze to make, but may be harder to find pre-made.

P.S. I am not sure about CAT-5, but on a serial cable, pins 2 and 3 represent the Tx and Rx lines (I do not remember which is which). On the other end of a normal cable, these pins are reversed. To make a null-modem cable, just pry open the connector and swap the position of these pins, and then put it back together.

Ask them to make you one. Just tell them that in lieu of flipping the Tx and Rx lines, to keep them straight thru.

Concerning a null-modem CAT-5 cable, I was able to buy one of these at Pantip (in Bkk). So I know they are available. If you are looking for a null-modem serial cable (RS-232), then these are a breeze to make, but may be harder to find pre-made.

P.S. I am not sure about CAT-5, but on a serial cable, pins 2 and 3 represent the Tx and Rx lines (I do not remember which is which). On the other end of a normal cable, these pins are reversed. To make a null-modem cable, just pry open the connector and swap the position of these pins, and then put it back together.

Hi Gumball

thanks a lot - does swapping the position of the pins require any special tools?

cheers

H.

thanks a lot - does swapping the position of the pins require any special tools?

Great advice from Gumball there. Odds are you'll have to get one made, as you generally can't switch the wires in a commercally made one. I guess there are a few of us old fogeys around who actually remember what a null modem cable is.

Made plenty of them in the past when more then modems started having RS-232 interfaces on them. Easy to make, soldering iron and wire cutters and wired up as below depending on the device requirement.

http://www.lammertbies.nl/comm/cable/RS-232.html

If D25 or D9, easier to buy an adaptor for a standard cable, like this:

http://www.pacificcable.com/NullModemAdapters.htm

Seeing what they look like (or print out the picture) you should be able to find one in a computer mall, even if the sales people have no idea what you're talking about. It should have 'Null Modem" stamped on it ! :-)

All the technical info necessary to solder D25 / D9:

http://en.wikipedia.org/wiki/Null_modem

You can tell if a Cat5 cable is straight through or crossover by holding the plugs together side by side. If the colour sequence in each plug is the same it's straight through, if not it's crossover.

Hi all

FYI, I managed to find a null modem cable on sale at a shop just outside Icon shopping centre (next to Computer Plaza). The shop's called 'Amorn', but don't look for the name in Western script - there's only Thai writing on the outside. It is to the left of the front entrance at Icon. They've got all sorts of electrical gadgetry and parts.

I think I may have got the last one available at the time, but hopefully they'll restock when they realise how popular they are these days.

Good luck.

H.