Bergmann@DMZRZU71.BITNET (09/12/89)
Can someone out there tell me, how a serial RS232 cable for the SLIP Packet driver has to look like ?? I am still having troube with baudrates > 2400 bd, I think due to handshake problems. (I want a IBM-PC to IBM-PC connection) Thanks H.-J.
bmw@isgtec.UUCP (Bruce Walker) (09/13/89)
In article <890911175832.602004@DMZRZU71-UNI-MAINZ--GERMANY> Bergmann@DMZRZU71.BITNET writes: >Can someone out there tell me, how a serial RS232 cable for the SLIP >Packet driver has to look like ?? I am still having troube with >baudrates > 2400 bd, I think due to handshake problems. > >(I want a IBM-PC to IBM-PC connection) After experiencing bitrate-related problems myself, I hooked up a scope and verified my suspicions -- that the serial ports themselves were distorting the signals above 4800 baud. The comm ports on PC's use 1488 and 1489 style RS232C line drivers and receivers. RS232 specs specify slew-rate limiting to minimize ringing and reflections on long lines. Some PC comm cards have this slew-rate control (in the form of small capacitors connected to the 1488's (and sometimes the '89s as well). Sometimes, it seems, the slew-rate control is excessive and puts a very large slope on signals above 4800 or even 2400 baud. This causes the pulses to become spikes and the receiver has trouble distinguishing these signal from noise and rejects them. If you have the schematics for your serial comm ports, you can determine if you've got slew-rate caps installed. If so, simply clipping one lead with small wiresnips will clear up your SLIP problems. For more information, I suggest you hunt down a copy of Motorola Semiconductor's Linear Data book. The parts in question are: MC1488 and MC1489A. Lots of other people make these things as well: Texas Instruments: SN75188 and SN75189A Fairchild: MC1488 & MC1489A (and others too numerous to mention :-) One of these (I think Fairchild) provides in their databook papers on the specs and transmission line theory involved. -- Bruce Walker ...uunet!mnetor!lsuc!isgtec!bmw "Better Living Through Connectivity" ...utzoo!lsuc!isgtec!bmw ISG Technologies Inc. 3030 Orlando Dr. Mississauga. Ont. Can. L4V 1S8