From: ia4@cunixa.cc.columbia.edu (Imran Anwar)
Newsgroups: comp.dcom.modems
Subject: Why is this modem cable's DTR mapped to RTS?
Date: 6 Sep 92 05:05:16 GMT
Reply-To: ia4@cunixa.cc.columbia.edu (Imran Anwar)
Organization: Columbia University


I have an EXTREMELY expensive, EXTREMELY unfriendly/unadaptable but
EXTREMELY effective proram for data transmissions from Mac to Mac using
ONLY Telebit Trailblazers at both ends.  The program is TOTALLY closed
and really horrible as a consumer product but the damned thing manages
to give me an AVERAGE of 9.6k transfers from NY to Pakistan using
Trailblazers.

BUT the problem is that the product has redial times of once in FOUR minutes
(which means, over international lines, taking as long as a couple of hours
before it actually gets a real connection. AND, when I hooked up my
new WorldBlazer with it the program did not work, or rather fails.

This is what happens with a Trailblazer:

It piks file from one designated folder, compresses it, and places it
in a designated outgoing folder.  Then it asks to Reset the modem (turning
on with T/D pressed).  Then it sends some data to the modem which basically
(from what I can tell) sends commands to make the modem quiet in dialing andf
not to echo, sets s58 and 68 to 2.  Then a few minutes later it dials.
If the connection is established (usually easier at 5 am then at 9 am :-(  )
it sends a quick stream of data with the bps rate column saying 19200 bps,
(this is probably some header information it sends) and then it sends what
I think are fixed length packets of about 30kbits in a big burst, when it
does that the modem's CTS and SD lights go on.  It probably received a small
single acknowledgment for that burst and sends the next one until the file
is complete.  It then does the next file, and finally discosnnects.

When I connected the WorldBlazer it sends out apparently the same strings as
before but a few crazy things happen.  It says dialing, then it says Code
0 Detected, Trying Again.  And goes back to waiting.  AFTER that the World-
Blazer turns ON, dials the nuumber, and instantly hangs up!  i.e. a delayed
response.  This keeps happening over and over again.


Among other things I asked Telebit tech support (very helpfful) was about
if the Result codes were different between the TB and WB modems, they said no

But , despite attempts, we could not figure out what was happening.  I did
remember that the program ONLY works with a modem cable the company gave.
And one of the things I noticed between this and other modem cables I had
was that with it the Modem Ready light and CTS come on but NOT the DTR light.

Interestingly, when this cable is hooked to the Worldblazer the RTS light
comes on (the Trailblazer Plus does not have an RTS light or I would have
noticed this sooner). instead of the DTR light.  When I make any other
communications program eventhen the RTS light comes on instead of DTR.  And
"inverting DTR" in the application makes the RTS light go on and off.

That really suprises me.  Could this have any implications for fast data
transmission, because when I use ordinary hardware cables with the
Trailblazer or with the WorldBlazer and send data to the same numbers in
Pakistan with any other standard program like White Knight, Microphon etc
using X-, Y- or Z-modem in all the cases the file transfers fail, or
achieve 80 cps or even lower :-(

I am totallyt confused if it is just some super programming that they
employed and is it related to DTR/RTS switching on the cable or is that
kjust a trick to sell expensiuve cables.  The company is in England
and they want about $5000 yes that is $5000 for an UPGRADE!

The program shows that it is based on the Think C libraries so I am not
evenm sure if the Think C code has some such standard high speed data
transmission routines.

Hope people on the net can please help me out with this.

Thanks

Imran