Diacom plus on Pentium laptops

[Lawrence King]

Dear all:

I took a look at the timing diagram for the 160 baud data and at Ludis
Lanagens idea. The first low period looks like a standard 'start' bit
and lasts for 200uS. If you assume 200uS is one bit time it gives you
a baud rate of 5000 bps (1/.0002). A standard UART should have 4800
bps available which is close enough for serial data.

If you program the UART for 4800 baud you will get one character for
each bit that the ALDL sends. The character will either be a 0xFF when
the ALDL sends a one (1) bit or something else for a zero (0) bit. The
zero bit may come into the system software as 0x00, or a 'break'
signal, or a framing error, depending upon your operating system
software and the UART on the system (but a zero will always be one of
the three possible results).

I am not sure if you need the signal level inversion or not (I can
never remember which way is the idle state for RS-232) when you send
the ALDL signal to the RxD pin of the serial port, and you may not
need the level conversion since most modern RS-232 chips consider 0v
as a low and 5v as a high. In the worst case you would need level
conversion and inversion.

It should be possible to receive this data with any standard UART
under any operating system which supports 4800 baud. This is
independant of processor speed. Some operating systems may discard
characters with errors (framing error or a break signal), in which
case you would need something like the PIC microcontroller.

Hope this helps you out.

		-Lawrence-

steve ravet wrote:
> 
> jdzura at csc.com wrote:
> >
> > >Ludis Langens did have a clever idea for using a serial port to talk to
> > >both, maybe someone should forward the idea to Diacom...
> >
> > I'm interested, What was the clever idea.
> >
> > Joe
> 
> Well, here's the link to Ludis' post:
> 
> http://efi332.eng.ohio-state.edu/diy_efi/archive/archive_num_94;lines=8695-8786
> 
> The whole thread was called "GM ALDL interface", you should be able to
> find it in subject line search.
> 
> The way 160 baud ALDL works has been posted many times, here's a link:
> 
> http://efi332.eng.ohio-state.edu/diy_efi/archive/archive_num_77;lines=5733-5824
> 
> I posted a longer explanation myself a long time ago, but I can't seem
> to find it in the archives.
> 
> --steve
> 
> --
> Steve Ravet
> International Meta Systems
> http://www.imes.com
> steve at imes.com

-- 
Lawrence King	Ottawa Ontario Canada
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