Re: [ProgSoc] Serial cables.

[Christian Kent <ckent@nospam.socs.uts.edu.au>]

On Sat, 20 Jun 1998, Richard John Vagg wrote:

> > > If thats right are you using the same program on both computers?
> > Absolutely not.  But that's not within the scope of this thread  :)
> Well... I guessed the cable might be the problem but there is nothing
> saying the problem is not in the Laptop. And it is sounding more like that
> now.

Someone else is using the same hardware and software but with a PC Card
modem, whereas I'm going cheapskate with an old external 28.8, so now I'm
finding difficulties.  Prolly the cable, IMO.

> > I tried &D0 and &K4, with no joy just now.  Though I did get a local echo
> > of what I was typing without using the terminal program's local echo.  Not
> > sure if this used to be the case, yech.
> So the Laptop was recieving characters that you typed... Well i can think

Yeah.  For a moment I thought about dismissing this point, but then I
unplugged the cable and found the characters stopped.  It started echoing
again when I plugged it back in; and when I turned on the terminal's local
echo, I got double chars, plus control char sequences for arrow keys etc
etc.

> of two things that would do that. The obvious one is the modem is echoing
> back the characters that you type, which is what you want it to be. But I
> have another option niggling at the back of my head, that TD and RD are
> linked somewhere, but it couldn't be that could it. 

Ummm.  Let's keep this option open though.  I'm perplexed at the moment.

> If you type a single AT then return do you recieve an OK back?

Trust me, it's the first thing I tried.  There's an echo, but no response. 
I change plugs and type AT<cr> into Hyperterminal, and I get an "OK". 

I plug the laptop directly into the PC and Hyperterminal works too.
However -- big clue here -- this only works under Software or No flow
control.  Hardware flow control just locks up the side you're typing on,
for a few seconds.

Also, I think I can rule out the female-female contabulous fabtraption as
a factor ... I had the brilliant idea an hour ago, when I spotted a spare
Iomega SCSI cable, to use it because it had male DB25 plugs on both ends.
This meant I could try my dodgy 8-pin/6-pin cable together with the
female/female dongle (which was a common factor so far, in all my
successful attempts at communicating between laptop and PC) and plug all 3
into the modem and laptop.  Didn't work, same as before.

> Umm, on your laptop is the terminal program possibly looking for RTS/CTS
> control...

Umm, you mean hardware flow control??  <sarc off>  Not now -- like I said,
that was giving me bad luck.  Software or None gave me some sort of weird
echo with the modem ... but gee whiz, what's causing =that=??  No "OK"s.

> Don't suppose you have a break out box or a multimeter?

No;  and to answer your other question, I have to use a cable like the one
I've got on the laptop because of the 8-pin serial connector on my laptop.
But next time I buy an adaptor cable like this, I'll make sure the other
end has at least as many pins, not just 6!


Okay, can anyone link the absense of RTS/CTS pins on the modem side to (a) 
causing an echo back to data terminal but without any modem respsonse, (b) 
but only when hardware flow control is not used (else nothing at all)?

NB, prior turning off all flow control via AT&K0 made no difference.

> > > D0 is not neccessary as you have both DTR and DSR. You can leave it at
> > > &D3.
> > Shall try.
> Shouldn't make it work any better though.

Nope.


Thanks again!

CK.

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