What is the maximum length for RS232 serial cable?

[bluemax]

See sig. I have someone who wants a +100-foot DB9 serial cable and they don't seem to go beyond 50' from what I've found.

To make matters worse, he wants it to be a null-modem (crossover/interlink/etc) cable at that! (I have a tiny null-modem adapter if need be.)

 

[interchange]

You can pin out your own adapters no problem. The published spec is (I believe) 75 feet.

If you're having problems, you can get an RS-232 to RS-422 adapter and then RS-422 to RS-232...this will convert to differential I/O that will have better signal integrity.

What does he need this for?

 

[bluemax]

You know.... I'm not 100% sure what his app is, beyond industrial nature.

But we do have those RS232 - 422 adapters here.... maybe........ good thinking!

EDIT: Dang... it's the RS232-RS485 I have here. Don't think that'll help much....

 

[bluemax]

Looks like I found my answer. Official specs for 19200baud serial is only 50 feet,
Lower that rate to 9600 and you can get an absolute max of about 500 feet! Of course, for that distance I'll need super-high quality cable - something most of my vendors don't seem to be offering.

 

[interchange]

I've never used RS-485, but I think it's basically RS-422 with potentially multiple drivers on the same line. It's also differential and will therefore allow longer cabling. You should be able to use those adapters for your needs.