Now I'm sure I'm one of very few people here that still have any interest in the old SLC 100/150 line.. But I just discovered something new that I thought I'd mention.

Up till now, I was under the impression that you NEEDED a 1745-PCC (or equivalent) in order to plug your computer into a 100/150. I had always been told that the 100/150's comm port is RS422, and the interface circuitry converts RS232 to 422. So naturally I was sceptical when a guy on ebay had a listing for a cheap, simple serial cable for 100/150 communication. They were so cheap that I thought what the heck, I'll buy one just to see what happens. Well I'll be darned, IT WORKS!! The cable pictured below, just an ordinary serial cable with a DB9 on one end and a DIN-8 on the other, had me online with a 100. Now am I the only one that didn't realize this would work, or what? What's going on here?

Does he have any more. How cheap is cheap?

Would that happen to be this one right here?

http://cgi.ebay.com/Programming-Cable-for-...4QQcmdZViewItem


I have an RS232-422 coverter for a gage multiplexer that has a postage stamp sized board in the RS-232 end housing. I wonder if they did something similar.

That's the one! There's **NO** electronics anywhere in this cable though, let me assure you. The RS232 end is just a molded plug, there's no shell housing.

I would guess that it is just a matter of the 422 being loose enough to still detect the 232 high/low levels. Same thing has been noted using 485 networks without a pic box in other posts here.

electronics quiz!!!!
422 is a four wire interface operating at 5v. There are 2 xmit lines and 2rec lines. This is a differential interface so that one of the lines is high and the other is low (for both xmit and rec.) this eliminates (hopefully) spikes since both lines of a pair will normally be raised equally, so there is no differential, or the differential remains the same.

232 is a 2 wire interface running at 12v. There is 1 xmit and 1 rec. On some laptops, to save energy, the 232 ports were operated at less than 12vdc.

485 is a 2 wire interface operating at 5vdc. It is also differential but the xmitters are normally off and only transmit when necessary. Everyone is normally in 'listen' mode.

5v is at the lower end of the on/off transition for the 12vdc components. So, if you hooked up the 422 transmit line to the 232 rec. and hooked up the 422 receive to the 232 xmit it might work. Its pretty susceptible to noise however, and might also have other impedence considerations. Also as the 422 side can 'float'. theorectically the 422 side could be at 100vdc when referenced to the 232 side which is referenced to zero.