🚀 go-pugleaf

I need to access a computerized switching system (yes, I'm authorized!) via
a modem for testing purposes.  The system is intended for use by people, not
computers.  To gain access, you must dial an access code _after_ the first
ring, but _before_ the second ring.  This is a pretty narrow window to hit
accurately.

I have a modem made by Practical Peripherals which uses a set of three chips
made by Rockwell.  The IC numbers are: R5311-29, R5310-38, and 10464-16.
I'm assuming this is the much-touted "Rockwell Chipset" I've read about in
modem ads and reviews...

The modem has a command ("AT@") which waits for a ring followed by 5 seconds
of silence.  This is almost what I want, except that I can't wait 5 seconds.
(There would be another ring, and I'll have missed that window.)  I've tried
peeking at the 8051 code which drives the modem, but it's a big haystack and
a small needle to try and change that 5-second delay.

My best hope at this point is that the modem chipset will output a logic
level when some supervisory tone is detected on the line.  (Similar to the
function of the Teltone M980 IC.)  If I can find this pin, I can route it
out the RS232 port and detect the ring signals in the host software.  Which
pin would carry the signal I'm after?

Please note that I need to know when the _distant_ phone is ringing. 
Detecting an inbound ring is pretty simple.

Any help appreciated!

-----------------------------------------------------
Gordon S. Hlavenka            cgordon@vpnet.chi.il.us
Crash Electronics, Inc.                (708) 963-8088
140 S. Lincoln                  "A Westmont Tradition
Westmont, IL  60559              for Over a Quarter!"