DirectScan "RAM Scan Tool"

[Peter Gargano]

Someone just purchased the DirectScan Unit. It's described here:

  http://www.chuengineering.com/

and you can get the details on it as a PDF file from:

  http://www.chuengineering.com/manual.pdf

Reason I mention this is that someone was kind enough to send me 
a scan of the unit's 10 chip (74HCxxx) PCB. 

The unit plugs into the ECM's PCB edge connector where address,
data, and some control signals are available. DirectScan has RAM
(62256) and address multiplexers (4 x 541 tristate buffers), 
and some simple logic (257 mux, 590 counter, etc. to enable the 
PC's parallel port to read the RAM - and that's about it.

The unit's RAM "mirrors" the ECM's RAM, but it's not dual
ported (in the sense that while the PC is reading the RAM, the
RAM is not being updated). The other circuitry lets the PC read
the RAM - nyble by nyble. The rest of the package is the software
that interprets the RAM.

Neat, eh! More expensive that some ALDL scantools, but certain 
benefits exist!

Peter.
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