Re: Parallel Card

["Michael J. Mahon" <mjmahon@aol.com>]

Bryan Parkoff wrote:
> Matt,
>
>     Thank you for the explanation.  I am very curious about the timing on 
> Apple //e.  HAL16R8 chip contains 16 timing possibilities.  This chip has 8 
> inputs and 8 outputs and 8 registers as inside another 8 inputs.  I only 
> want to view 8 outputs.
>     How is it possible that game connector can be done?  I write assembly 
> language to send one byte as 256 possibilites from the memory to the game 
> controller.  Then HAL16R8 chip receives 8 inputs and transmits 8 outputs 
> back to the game controller.  Eight outputs is stored into memory.  I view 
> stored bytes in memory.
>     Do you have draft schematic that it might help me to design in my own? 
> Michael Mahon said that two parallel cards are only the answer.  I think 
> that game controller card might be a good idea for money saving.
>
> Bryan Parkoff

Actually, I said two parallel *ports* is the way to go to read a
device with 8 inputs and 8 outputs.

Those parallel ports can be implemented simply as a 6522 on the
Apple bus, or as two parallel cards (as long as at least one of
them is capable of *reading* 8 bits in parallel), or as two 8-bit
serial/parallel shift registers connected to the game port.

In the latter case, the shift register used for input will have
to have a "load" strobe supplied to sample the device outputs
prior to shifting them back for reading by the Apple.  It may also
be necessary to use output enables on the output shift register
if the device being "read" is sensitive to the *sequence* of
states applied to its inputs, so that the shifting of values
into the output port does not present the part with unwanted
states.

I suggested a "direct" parallel port approach because 6522
hardware is available already constructed and the programming
is simpler, but there are, of course, many other alternatives.

-michael

Music synthesis for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."