Occilliscope

[Roger Heflin]

On Tue, 28 Jul 1998 ARoss10661 at aol.com wrote:

> In a message dated 98-07-28 22:04:48 EDT, you write:
> 
> << If you want to do some electronics and a computer, you can get a cheap
>  A/D convertor (ADC820 I believe), and wire it into the paralell port.
>  You can do it without any extra circuitry except an external power 
>  supply to power the A/D.  The convertor is good for 600khz (good
>  enough for auto use) and with a PC paralell port (on a 486 or so) you
>  can get at least 20 khz or so out of it with quick basic.  If you
>  use something more serious (C or Assembler) you can get closer to
>  100khz out if it.    >>
> 
> If u could get a little more specific about this design I would appreciate it
> this sounds like it would be great!
> Al
> 
The trick is pretty simple.  There are 16 bits on the parallel port
(classic one way port).  The 8 output lines will only go out.  There are
8 control lines (5 are on one i/o port, and 3 are on the other i/o port)
that can go both ways.  You use the control lines for input lines from
the parallel out on the a/d and you use the 8 ouptut lines to give the
a/d the proper signals for it to work correctly.   I don't have a 
diagram on the computer, but some of the details are:

0x378 - Output for printer output lines
0x379 - top 5 bits are bidirectional (they have to be set to go in)
0x37a - bottom 3 bits are bidirectional (they have to be set to go in)

I got the info from a article on tricks using a parallel port.  I do
not rememeber what magazine it was in.  There may be a reference on
internet for it.

But the general ideal is that the wires that go with 0x378 are connected
to the control inputs of the A/d and then you send the right bits to
0x378 to pulse the controls of the a/d and then you read in the
data from 0x379 and 0x37a and mask and or it together.  

				Roger Heflin