Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!decvax!harpo!seismo!hao!hplabs!sri-unix!smith@nrl-aic From: smith%nrl-aic@sri-unix.UUCP Newsgroups: net.micro Subject: Request for help (long msg) Message-ID: <12956@sri-arpa.UUCP> Date: Tue, 25-Oct-83 07:37:00 EST Article-I.D.: sri-arpa.12956 Posted: Tue Oct 25 07:37:00 1983 Date-Received: Mon, 31-Oct-83 03:13:29 EST Lines: 70 From: Russ Smith This note is a request for info/help/suggestions about a peculiar problem I've been having with an I/O-board/external-modem setup on an S-100 system. Background: I have a GODBOUT (pre-COMPUPRO) Interfacer II serial I/O board controlling both the console (H-19 with Super-19 PROM at 19200 baud) and an external RS-232 port (at 1200 baud). A Hayes Smartmodem is plugged into the external port. The z80 S-100 computer is running at 4Mhz with no wait states. Problem: The above setup allows both a home-grown modem program and MDM712 to call up another machine and do their respective things. However, if I hang up (using the Smartmodem "ATH") and try to call again strange things happen...characters are being sent to the modem (modem lights flash on cue for example when I type "AT" on my terminal and the Smartmodem answers back with "OK") but no characters are being echoed to my CRT screen. This would seemingly point to a software problem, but I can't see where. Why? Below is an outline of the home-grown modem I/O sequence. The routines to get and put characters have been used in dozens of other programs without any trouble (and they work fine the FIRST time the program is run). read both the CRT and modem ports a couple times (initialization) LOOP FOREVER { IF a modem character is present THEN get the modem character and put it to the CRT ENDIF IF a CRT character is present THEN get the CRT character IF the CRT character is THEN exit ELSE put the CRT character to the modem ENDIF ENDIF } The above code implements a very simple full-duplex protocol. The CRT expects whatever gets its characters to echo them back. Indeed, in local mode the Smartmodem DOES echo them back (lights flash...) but NOTHING gets put on the CRT. Again, it only happens after I've done something and then sent "ATH" to the Smartmodem. I should mention that the Smartmodem is receiving the correct characters since it will dial a number, etc. The above problem also applies to the much-tested MDM712 modem program. Exactly, the same trouble. Works first time but can't hangup and try to dial again and expect characters to echo to the CRT. One other point...when the CRT is directly plugged into the modem the modem/CRT combination works beautifully at both 1200 and 300 baud. Absolutely no irregularities... Bottomline Questions: Does someone out there know of a peculiarity with the Interfacer or Smartmodem which could cause this problem? Is there some initialization sequence (other than just reading a couple characters from both ports) which you've found is necessary? Has anybody had a similar problem with either the Interfacer (not really suspected, it's a rock) or the Smartmodem? Does the Smartmodem do some RS-232 status line twiddling which it's expecting to be twiddled back at when it hangs up? HELP!! Please send any info/help/suggestions directly to me. If it turns out that there is some strangeness with the Interfacer/Smartmodem that isn't documented in the manuals, I'll send a follow-up message to the list. IF YOU HAVE ANY IDEAS, PLEASE RESPOND! Thanks in advance, Russ