ALDL Communications...

[Gary W Harris]

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Don,

The serial data is 0--5 volt simplex, and needs to be converted to RS-232 for 
the PC.  I use a maxim chip powered from a 9-volt battery to do this.  A diode 
and pull-up resistor are also necessary to "wire-or" the PC TxD to the ECU's 
simplex data line.  This works great!  I have a schematic, but it's in Viewlogic
format.  I can snail-mail you if you send me your address.

Gary Harris

A while back, several of you guys were hooking up your ALDL serial
connectors to your pc's ...  I believe I even received a copy of the
software to change the pc serial port to something near 8192 baud...
What I was wondering (since I'm planning to try to hook mine up
this weekend and do some reading) is what the signal levels are
on the aldl serial line ...  Is it 0 to 12v or is it 0 to 5v??  And,
is it inverted??  I was thinking about using either MAX203 or MAX233
RS-232 signal level converters, but they are designed for 0-5 with
standard non-inverted inputs ...  If it is inverted or is 0-12
instead of 0-5, I'll need to put a transistor or two on the front
of the MAX chip to change it's level and/or polarity...  Either way
is no big deal and I'm hoping someone can answer this so that I
won't have to drag the oscilloscope outside to check it...

Thanks ....
Donald Whisnant
dewhisna at ix.netcom.com

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