🚀 go-pugleaf

In article <5821@fortune.UUCP> mats@fortune.UUCP writes:
>
>Well. modems have the characteristic of only supplying a ready
>signal to the outside world when a connection is established.
>This is good and proper behavior - you don't want to try to
>talk through the modem until there is something on the other
>end. But the poor terminal/system can't even send the "transparent" 
>commands to the modem until it sees this ready signal - like you
>can't send out the commands to establish the connection until
>the conenction is established (don't they call this Catch-22?). 
>So what to you do? Well, the modem makers tie the signal permanently 
>high so they can guarantee the terminal can always talk to the modem's
>ROM and make it dial.
>

Not totally true... You do need to have a ready signal to send commands
(DTR is high), and a lot of modems have a switch to tie it high (e.g.
Hayes, Pro-modem, USR Password). If you wire the thing correctly (pins
2,3,7,20 - I think that's what we use), you won't have that problem. Pin
20 is the DTR pin and it's supposed to be set high by the host computer.
This is done (or should be) when you 'open("/dev/ttyxx", ...)' the modem
for dialing out. As soon as you close it, it drops DTR. Also, on modems
which are for dial in, I think that if DTR is not always tied high, when
the carrier is lost, a hangup signal should get sent to the attached
process. At any rate the solution is as follows:

	1) Make sure the DTR switch on the modem is set so that
	   DTR is *not* always tied high.

	2) The rs-232 cable has pin 20 (DTR) wired from the modem to 
	   the machine.

	3) Make sure your device drivers are supporting DTR. If not,
	   you're outa luck!

-- 
* Isaac Salzman (Gumby)
* Research Development Labs (RDL)
* Culver City, California, 90230
* UUCP: ...{ttidca,psivax}!rdlvax!salzman
* ARPA: ttidca!rdlvax!salzman@Rand-unix.arpa