Path: utzoo!mnetor!uunet!oddjob!hao!gatech!uflorida!codas!burl!wrcola!rbdc!andy
From: andy@rbdc.UUCP (Andy Pitts)
Newsgroups: comp.dcom.modems
Subject: Re: Getting a Trailblazer's ATtention (Was Re: Trailblazer, flow control, DMF32)
Message-ID: <203@rbdc.UUCP>
Date: 18 Feb 88 08:02:04 GMT
References: <272@coherent.uucp> <3249@cbmvax.UUCP> <10433@mimsy.UUCP> <5445@elroy.Jpl.Nasa.Gov>
Distribution: comp
Organization: Red Bard Data Center
Lines: 58
Keywords: telebit trailblazer emulex 19200
Summary: Your making it more dificult than it is

In article <5445@elroy.Jpl.Nasa.Gov>, stevo@elroy.Jpl.Nasa.Gov (Steve Groom) writes:
> In article <15547@onfcanim.UUCP> dave@onfcanim.UUCP (Dave Martindale) writes:
> >I've written a Telebit driver for 4.3BSD uucico.  After opening the line,
> >it does:
> >
> >	for (i = 3; i > 0; i--) {
> >		sendthem("A\\dA\\dA\\dA\\dT", dh);
> >		if (expect("OK\r\n", dh) == 0)
> >			break;
> >	}
> >
> >	[discussion about extra A's deleted -slg]
> 
> I spent a lot of time trying to come up with a dependable way to do
> this, and I too decided to try putting the AT sequence into a loop of
> retries.  However, I eventually concluded that a simple loop like this
> would not work reliably, no matter how many A's were in the attention
> string.  [...]

Getting the Telebit to autobaud is easy.  I think this has been discussed
here before, but let me quote a section of the manual:
_____________________________________________________________________
"When S51 = 255, the modem will try different transfer rates until it
receives an upper or lower case "A".  It then selects a transfer rate
and begins to echo characters.  [Stuff deleted].

The modem will go into speed select mode in the following  situations:

1.  If the value of S51 in the non-volatile memory is 255 and the modem
    is powered up or reset (ATZ).
2.  If S51 is changed to 255 while in Command Mode.
3.  If S51 is 255 and a break is sent to the modem from the local DTE
			^^^^^
    while the modem is not connected to another modem."
_______________________^^^____________________________________________

I have found the following code reliable for getting the Telebit's attention:

{
	.
	.
	.
	(void) ioctl(fd, TCSBRK, 0);  /* send a break to the modem */
	(void) sleep(1);
	for(i = 0; i < 7; i++)        /* send some A's with a 1 sec pause */
	{
		(void) write(fd, "A", 1);
		(void) sleep(1);
	}
	.
	.
	.
}

This sends a break, and a string of "A"'s (with a pause between them).
It works every time, and you don't have to muck with DTR.

Andy Pitts       {gladys, bakerst}!rbdc!andy