phys169@csc.canterbury.ac.nz (04/05/91)
In article <1991Mar26.160343.14686@unx2.ucc.okstate.edu>, uccxmgm@unx2.ucc.okstate.edu (Martin McCormick) writes: > > We have a most exasperating problem with an IBM PS2 > Model 70 running MSDOS 4.01. The system has a ROM BIOS > copyright date of 1988 and has been working perfectly for > well over a year. I recently wanted to use it with some > applications which required operating the system through the > serial comm port. I discovered that I couldn't make the > CTTY command work at all. I could run "Kermit" and > communicate back and forth between the PS2 and another unit, > but try as I might, I couldn't get CTTY to work. Almost certainly the answer is: You haven't got the modem signals right. You should have a good positive voltage (say, 10v) on pins 4,5,6,8 & 20. Some of these are outputs. Good communications software like Kermit sets outputs correctly and ignores floating "clear to send" and such like signals if it has to, CTTY and COPY don't. The solution is to connect across all those signals you've missed, being careful not to connect outputs to outputs. If you had to swap 2 & 3 then connect 4 of one end to 5 of the other, and 6&8 together to 20 of the other, otherwise connect all lines straight through. If this doesn't work, get a multimeter or similar tool out and see what signals are wrong. Notice that the PC changes the output lines as you start up CTTY or whatever, and looping back 4 to the 5 of the same plug (a good trick on most terminals) doesn't always work... perhaps due to timing problems? When using CTTY, watch out - the DELETE key on terminals sometimes causes strange behaviour on the console screen. Anyone else found this?? Mark Aitchison, Physics, University of Canterbury, New Zealand.