Re: John Bell A/D converter

[mjmahon@aol.com (Michael J. Mahon)]

George Rentovich asked:

> Does any body have the Instuctions for one of these. Or the software
>for these. That would be a 16 channel  A to D converter by John Bell
>Engineering 81-132 copyright 1981 Made in the USA. Has 2 16 pin sockets,
>that  have DB 9s sodered to the other side with 2 resistors 10,000 ohm
>reistors on each DB 9.

I believe that this A/D converter is just two 8-channel A/D converter ICs
of fairly conventional design.  Look up the data sheets for the A/D
converter chips and you'll be 90% of the way home.  They probably
use the device select addresses to set the conversion channel and
trigger a conversion ($C0sX, where s = slot + 8).

I don't think that John Bell used an on-board ROM.  The A/D converters
are operated by software loaded in Apple II memory.  You can confirm
this by the absence of a 24-pin EPROM on the card.

-michael

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