Subject: From: Date:

Prairie Digital Model 40 Dan Carrington Mon, 15 Mar 1999 17:54:42 -0800

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	I had commented on this unit previously and had made medium remarks to
it as I had had some troubles in using it.  I would like to up my
impression of it.  I had received a few instructions from someone on the
list (I don't remember your name, but thanks) and I have now gotten mine
working happily.  It seems that to use all 28 Digital I/O's, you need to
not only not jumper the SPI (analog enable), but you need to also remove
two chips on the circuit board that tie onto some of the top I/O's
circuits (C4 through D3).  
	Mark, you may want to add this part to your instructions as I can not
find anything about it in ecs.htm.  Things such as, if you use the
analog convertor and analog inputs, you will lose C4-C7 and D0-D3
I/O's.  If you use the multi-plexor (I don't know what this does for
you) you will lose C4-C7 as the multi-plexor is also tied to these
lines.  These things are not documented through ECS.  But this info is
directly from deep within their manual on the Model 40.
	I have now removed the analog convertor chip (8 pin DIP with # 549 on
it) and the multi-plexor chip (16 pin DIP with 4051 on it) and set them
aside and now all 28 of my I/O's work fine.  Also remember that you need
to install resistors on the circuits if you are planning to use them as
an input.  I use a 2 megohm resistor between each I/O that is set to
input and ground.  Now when I apply power, it switches, and when I
remove power, the resistor allows it to bleed off and switch back. 
Otherwise they can float for a while before expending their power by
bleeding off internally.  Overall I use 21 of the I/O's as outputs
driving relays through a transistor to power the coil and the other 7 as
digital inputs.  All is now happy.


Dan Carrington

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