fair@dual.UUCP (Erik E. Fair) (07/11/84)
>> From: brahms@trwspp.UUCP >> Newsgroups: net.micro >> Subject: Hayes Smartmodem carrier detect >> Date: Mon, 9-Jul-84 18:28:46 PDT >> Organization: T R W, Redondo Beach, CA >> >> Is there any way to make the Hayes Smartmodem drop carrier detect (pin 8) >> when it detects loss of signal? Even a hardware hack would be acceptable. >> >> On page 7-12 of the Hayes manual it states: >> >> "The Smartmodem 1200 will always act as if a carrier is present". >> >> This makes it impossible for the system to know if the remote modem has >> hung up. Thanx for any help you can give. >> >> -- Brad Brahms >> usenet: {decvax,ucbvax}!trwrb!trwspp!brahms >> arpa: Brahms@USC-ECLC Time for lecture #1 on autodial vs. answer only modems and computer modem control. First some background on modem control: Some Definitions: RI -> Ring Indicator (Someone is calling us on the phone!) CD -> Carrier Detect (Someone is actually there, complete with carrier) DSR -> Data Set Ready (Hello computer, I'm ready (modem)) DTR -> Data Terminal Ready (Hello modem, I'm ready (computer)) The proper way to do modem control on answering (the electrical signals): MODEM COMPUTER (periodically scans for RI) RI (I'm calling yooouooou!) DTR (OK, answer the phone) DSR (OK, I'm answering the phone) (wait for CD) CD (Someone is giving us a carrier) (print login banner and converse) ``Frobozz Inc 4.2 BSD UNIX'' This sequence gives maximum control of the modem and the conversation to the computer. Among other advantages, the modem will not answer the phone when the computer is down or if the software has been told not to answer. Most computers on the low end of the price spectrum, however, do things this way: MODEM COMPUTER DTR (``always answer the phone'') (periodically scans for DSR) RI (I'm calling yooouooou!) DSR (OK, I'm answering the phone) CD (Someone is giving us a carrier) (print login banner and converse) ``Frobozz Inc 4.2 BSD UNIX'' Note that the computer doesn't care about CD. It watches for transitions in DSR signal instead. Since answer-only modems of recent manufacture seem to raise and lower DSR along with CD, this is not a problem. It does tend to make the hardware in the serial interface and the software a little easier to deal with, since all you do is tweak DTR and watch DSR. What does this have to do with autodialing modems and such? Well hold on, I'm getting to that... With new autodial modems you have a paradox. You have to converse with the modem before there is actually someone there (remotely, that is) in order to get it to dial. In order to fool the computer (particularly one that follows the poor man's modem control as detailed above), the modem must assert DSR whenever DTR is asserted, in order to let the computer talk to it. With the rich man's modem control, and depending upon the sophistication of the software, you should be able to tell the difference between talking to the modem (DSR only) and someone remote (DSR and CD both asserted). HOWEVER! Should you desire that your extremely intelligent autodialing modem should only answer the phone (and that you should be able to tell when someone has hung up), what you need to cause the modem to do (particularly with poor man's modem control) is to raise and lower DSR along with CD. Note, however, that this effectively prevents autodialing, because you will only be able to talk to the modem when someone is there on the other end. I believe that the DC Hayes Smartmodem 1200 has this as a configuration option somewhere on the back dip switches if you read the manual very carefully. If not, I suggest that your login process have a 5 min timeout after which the computer will drop DTR to get the modem to hang up the phone. If your modem won't do that, then you're really out of luck... To reconsider this statement: >> On page 7-12 of the Hayes manual it states: >> >> "The Smartmodem 1200 will always act as if a carrier is present". I interpret this to mean that DSR will always be raised when DTR is asserted by the computer in order that you can talk to the modem to get it to dial. another eddy in the muddy waters... Erik E. Fair ucbvax!fair fair@ucb-arpa.ARPA dual!fair@BERKELEY.ARPA {ihnp4,ucbvax,hplabs,decwrl,cbosgd,sun,nsc,apple,pyramid}!dual!fair Dual Systems Corporation, Berkeley, California
hoffman@pitt.UUCP (07/11/84)
But it *does* toggle pin 8! You quoted only one sentence from page 7-12 in the Smartmodem book. THE VERY NEXT SENTENCE answers your question. Here's the whole paragraph: Setting S10 to 255 will cause the Smartmodem 1200 to ignore carrier detect status. The Smartmodem 1200 will always act as if carrier is present. However, the CD indicator light and the RS-232C Carrier Detect line will follow the true carrier status. What all this means is that if you set S10 to 255, then the modem does not hang up on carrier loss, but indicates the loss through pin 8. It's up to your program to sense this and drop DTR and hang up the phone. -- Bob Hoffman Pitt Computer Science
msc@qubix.UUCP (Mark Callow) (07/11/84)
I don't know what you were smoking when you read the manual....
If you set dipswitch 6 down you get the behaviour you mention.
If you set dipswitch 6 up pin 8 will folow the state of the carrier
on the phone line.
Read Table 3 on pages 8-3 and 8-4 of the manual.
You took the statement
"The Smartmodem 1200 will always act as if a carrier is present".
totally out of context. It was describing the behaviour when
you set the timeout value in *register* s10 to 255.
Mark
--
From the TARDIS of Mark Callow
msc@qubix.UUCP, decwrl!qubix!msc@Berkeley.ARPA
...{decvax,ucbvax,ihnp4}!decwrl!qubix!msc, ...{ittvax,amd70}!qubix!msc
"Nothing shocks me. I'm an Engineer."john@ecsvax.UUCP (07/12/84)
If you set Switch 6 on the Hayes UP, the modem will "determine if a carrier signal is coming from a distant modem by reading the status of the RS232C Carrier Detect lead (pin 8)." (page 8-3 of the manual) It is only if you set register S10 to 255 that the modem will ignore carrier detect status. Register S10 "Sets [the] time between loss of carrier (distant modem hangs up) and disconnect by Smartmodem 1200" (page 7-12). Setting S10 to less than 255 will allow the modem to react to loss of carrier. The default for S10 is 7. john hogan nc educational computing service rtp, nc 27709 (919) 549 0671 ...decvax!mcnc!ecsvax!john ...akgua!mcnc!ecsvax!john
perl@rdin.UUCP (Robert Perlberg) (07/12/84)
<> What we have here is a case of misreading. Here is the complete manual entry: Page 7-12: This delay time allows the carrier to momentarily disappear without causing the modem to disconnect. The value assigned to S10 is adjustable in tenths of seconds. The default value is 7 for a delay time of 700 milliseconds. Setting S10 to 255 will cause the Smartmodem 1200 to ignore carrier detect status. The Smartmodem 1200 will always act as if a carrier is present. However, the CD indicator light and the RS-232 Carrier Detect line will follow the true carrier status. end_of_extract Need I say more? If you had taken the time to read the whole paragraph instead of just one line you would have seen that the statement in question is conditional on your setting S10 to 255, a very special case. Not only that, the last sentence indicates that the RS-232 carrier detect line will ALWAYS indicate carrier detect whether you are using this option or not. If your carrier detect line is always TRUE, it might be because dip switch #6 is down (see page 2-6). Robert Perlberg Resource Dynamics Inc. New York philabs!rdin!perl
brahms@trwspp.UUCP (07/12/84)
[}{]
When I sent out my original message stating my problem with carrier detect,
I failed to add that I had set pin 6 correctly, thus leading to my query.
As of this point in time, I believe that the modem was bad. I will be trying
another one shortly to see if the problem goes away.
Thank You to all of you who replied.
-- Brad Brahms
usenet: {decvax,ucbvax}!trwrb!trwspp!brahms
arpa: Brahms@USC-ECLC