RICK@mit-mc.arpa (01/23/83)
From: Richard P. Wilkes <RICK@mit-mc.arpa>
{I apologize if people get repeats. The mailer croaked on the
address fylstra at SRI-TSCA. I don't think it mailed to the
list, but who knows...}
I have the Hayes 1200 and am very pleased with it so far. The
only problem I had is that the first unit I received died
after 2 hours. Hayes replaced the unit after a little griping
about a two week service turn-around on a modem I'd had for
one day. Apparently, things are a bit confused down there
(Georgia). The company recently moved across the street into
a new building.
<This info applies to both Smartmodems>
The Hayes has two modes: command mode and online mode.
In online mode, all characters sent to the modem are sent also
to the comm line. After dialing a telephone number and
detecting a carrier, the modem goes into this mode. It
notifies the computer (or terminal) by returning a result
code. The result codes are either verbose (i.e. CARRIER, NO
CARRIER, OK) or terse (ascii 30H-35H --0-5). Selection is
done by the users.
When in command mode, commands are sent to the modem by
preceeding them with AT which lets the modem determine the
baud rate, parity, and word length. The command follows. The
command terminator can be set thru software. The default is a
carriage return.
When the system is "online," the modem is put into command
mode by sending three "escape" characters followed by a pause.
The default escape character is "+". BTW, the escape
characters are passed thru to the online system. Because of
this, people complain about having to send "garbage" down the
comm line to to get the modem to do anything. However, I
don't see any other way to use one port and be able to send
the modem commands while online. Many modems do not allow
commands to be sent while online. The Hayes, since it allows
you to select which character is the "escape" handles it the
best way that I can see. The manual seems to say that either
end of the link can send the escape sequence. This bothers me
and I have yet to be able to confirm it. You can set the
modem so that it doesn't accept commands while online and do a
disconnect using DTR (I believe).
Here's a brief example of connecting to a system using a
program to send the commands:
1) Send ATZ (reset)
2) Wait for OK. If no OK, send escape and wait for OK.
3) Set up modem params (duplex, dialing rate, escape codes,
default line end (CR and LF -- easier to detect result codes
in the data stream)
4) Send dial command
5) Wait for result code.
6) If connect, go into data mode. Otherwise, No connection or
error (shouldn't happen unless the program is bad)
7) Send data. Check CD (carrier detect). When dropped, look
for No carrier result code indicating lost connection.
To hand up, send escape, wait for result (toss echos), then
send ATH (hang up), wait for OK.
I have found that since the Smartmodem is designed for "human
speed" commands, when sending commands to the modem, use echo
mode and wait for each character to be echoed before
continuing.
All in all, I really like the modem. The only negative about
the 212 part is that if you are using it as an answer modem,
it does an auto-speed detect and switches speeds. The result
code it sends is at the speed that the last command was sent
at, but then the modem may SWITCH SPEEDS to accommodate the
calling speed. The program must be set-up to reset the uart
to the appropriate speed or the modem and RS232 will be out of
sync.
BTW, the modem does morse code also...
Let me know if you have any more questions. The documentation
is acceptable and just about everything is software
selectable! -r