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sdbartho@c ==> Re: ALDL

From owner-diy_efi  Wed Mar 22 16:54:26 1995
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To: DIY_EFI
Subject: Re: ALDL 
In-Reply-To: Your message of "Tue, 21 Mar 95 09:04:33 PST."
             <"2558*rodb@cs.ubc.ca"@MHS> 
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Date: Wed, 22 Mar 95 10:53:49 -0600
From: sdbartho@cca.rockwell.com
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> ps.  This would be a good FAQ if someone was interested in the subject.
> 

I was thinking the same thing. Anybody want to start one? :)
 
> >
> >The ALDL uses a TTL level output (1=H=5V, 0=L=0V) with 8192 Baud.
> >A word consists of 10 Bits, the startbit (L), 8 data bits (LSB first) and
> >one stop bit (H). The line is idle high.
> >The ECM sends packets that look like this:
> >
> >1 byte device code
> >1 byte: 85+N (N being the length of the data part of the packet)
> >N data bytes
> >1 byte checksum
> >
> >between two packets the line goes idle (H) for at least 10 bit times.

This is a little misleading, from what I've seen on the 8192 format.
It may be correct for the ALDL data output in 10k mode.
It should read:

1 Byte message ID 
1 Byte Length (85 + 1 + N - The next byte counts too!)
1 Byte Mode Specifier ( Usually ranges from 0 to 7)
Data bytes
1 Byte checksum (two's complement of sum of the previous bytes)

> >Information still missing includes: A list of device codes,

This is defined in the Cal section of the PROM, and can be anything from
0-255. The ones I've seen seem to like to use 0xF0, and it normally will
be the same as the value of the heartbeat sent out in normal mode.

> the interpretation
> >of the data bytes and how to compute the checksum (which I probably could
> >find out myself... I guess it's just adding up the data part of the package.

See above. Knowing the proper mode ID's to send helps a bunch, too.

Anybody know of a good 5v to 232 converter with tri-state outputs? I've
been looking at the MAX 242, but I need to be able to ts two channels
independantly, and I only need two channels. I could always add an analog
switch, but I'd like to stay with a one-chip solution.

Dig
sdbartho@hwking.cca.rockwell.com