On Sat, 14 Apr 2001, Mike Ford wrote:
["Smart Cable" for "ANY DB25"]
> Actually I think it is supposed to be smart enough to handle serial/modem,
> and I don't know about current loop. I haven't tried it with SCSI either,
> but stranger things have happened. I think its called a smart comm so
> likely SCSI is out.
Not just "likely", ABSOLUTELY!
When you are ready to try it for non RS232 stuff, such as parallel, SCSI,
current loop, etc., please do the experiments on something disposable,
such as a current "state of the art" PC, or using disposable ISA cards and
printers, etc. Please don't toast any classics.
Let's look at HOW you would design something like that to work. It does
NOT connect all 25 wires, so it CANNOT possibly work for SCSI, parallel,
etc. It attempts to come up with the right combinations of pins
1,2,3,4,5,6,7,8, and 20. 1 and 7 are ground (chassis and signal). It
needs to take pins 2 and 3 ("Transmit" and "Receive") and decide whether
to send them straight through or cross them over. Then it needs to
figure out which ones of 4,5,6,8, and 20 need to be passed through, which
need to be crossed over with others, and which need to be looped back to
others on the same side.
A well designed circuit can do some wondrous things, but will still have
major limitations. Many of the weird corruptions of the RS232 standard
will not be supported. Hence, they would NOT work on the things that I
was trying to do.
For programmers with soldering irons (such as myself), "The RS232
Solution" by Joe Campbell from Sybex provides a good help towards getting
RS232 cabling to work.
BTW, there IS a documented fatality from the frustrations of serial
interfacing.
--
Grumpy Ol' Fred cisin_at_xenosoft.com
Received on Sat Apr 14 2001 - 16:46:23 BST