Serial Cable - IBM3151 to Sco Unix

[CranberryBlue]

I'm trying to cable an IBM 3151 terminal to our Sco Unix box. The line is configured as xon/xoff. It seems I need more than 2<->3, 3<->2 & 7<->7. Can I add jumpers on both ends (4-5 & 6-8-20) or do I need: 2<->3, 3<->2, 7<->7 & 4<->5, 5<->4, (6-8)<->20 & 20<->(6-8)?

 

[daronwilson]

If you havce enough wires between the two, i would implement full handshaking on the CTS/RTS and DTR/DSR lines, just to rule that out. If you don't have enough wires in the cable, you can certainly 'loopback' the ends and fool the devices. However, if you do this, you have bypassed hardware flow control and can overrun some buffers. But then ... you say you are using Xon/Xoff which is a software flow control, so maybe the lack of hardware flow control is not an issue.

Gotta love RS-232

Daron J. Wilson, RCDD
Solving 'Real World' problems

 

[CranberryBlue]

RS-232C Rules!

Anyway - I'm just confused as to why I need the hardware busy lines if I'm using xon/xoff flow control. A null modem cable works but I want to use RJ45F to DB25M connectors on both ends. 8 wire cable should give me enough.

 

[daronwilson]

IF you are in fact only needing Xon/Xoff, then you don't need the hardware flow control or loopback pins at all. However, I understood your post to say that you were using software flow control but did not have connectivity (i.e. something on the hardware side might be holding you up). RS-232 must be the worst implemented 'standard' i've seen, i've seen it everything from data and ground to 15 or more wires required for various functions. Everyone implements the portion they need, hardly a standard.

One manufacturer ASSURED me that they do NOT use hardware flow control. I spent an hour on the phone with him hooked to the PBX waiting for data to come out, changing settings, making phone calls. I finally grabbed my breakout box and tried changing state of one of the hardware pins and Shizzle! it worked. Apparently they don't implement hardware flow control but need the hardware flow control pin in a 'ready' state before they send any data.

Good Luck!

Daron J. Wilson, RCDD
Solving 'Real World' problems

 

[wires]

Try connecting pins 4 to 5 and 6 to 20.