Re: Apple II Parallel Cards

["Greg Andrzejewski" <pressyourluck85@yahoo.com>]

"Michael Black" <et472@FreeNet.Carleton.CA> wrote in message 
news:ed6s8i$pu9$1@theodyn.ncf.ca...
> "mdj" (mdj.mdj@gmail.com) writes:
>> Michael J. Mahon wrote:
>>> Greg Andrzejewski wrote:
>>> > Were there any parallel interface cards made for the Apple II that
>>> > completely adhere to the IEEE 1294 standard? Most of the ones I've 
>>> > seen seem
>>> > to missing/ignore some lines (nERROR, nSELECT, etc)
>>>
>>> Apple parallel cards were designed before there *was* a PC!
>>>
>>> IBM chose not to adhere to the Apple standard.  ;-)
>>
>> :-) and the 1294 standard was introduced about the same time as the
>> first Pentium PC's in 1994.
>>
>> I don't recall any of the parallel ports implementing bidirectional
>> signalling, either. The exception would be the ProFile controller card,
>> but this was not strictly speaking a parallel comms card of course.
>>
>> Such a card could be very easily put together though - the PC style
>> parallel port is a very simple interface. I seriously doubt though that
>> the Apple II would have the processing power necessary to communicate
>> in ECP or EPP mode with any peripheral that required it
>>
>> Matt
>>
>
> I didn't recognize the standard number, but it struck me that likely
> it had come later.
>
> Remember, the "IBM PC" parallel port was not two-way for a long time.
> When people needed both ways (for non-printer use), they'd get by
> with the input lines that were there (not a full byte's worth) in
> the form of handshaking lines.  Or, one article (I think it was in
> Micro Cornucopia), showed soldering some ICs onto a parallel card,
> to add 8 bits of input.
>
> You generally didn't need bidirectional on a parallel port, since
> they were printer ports, and it was easier to use an 8-bit latch
> than anything more complicated.  If you needed parallel input,
> you'd buy a card that used something fancier, and it would be classed
> as a parallel port, rather than a printer port.
>

Exactly. I/O from the parallel port doesn't require ECP/EPP. On IBM's SPP, 4 
status lines are used to read a nibble from a device (creatively termed 
'nibble mode'). A decent description can be found here 
http://www.fapo.com/nibble.htm. Using nibble mode allows the SPP to 
interface with more than just printers (tape drives, scanners, zip drives, 
etc).

The problem is the lines used by nibble mode aren't present on most Apple II 
parallel cards. If there was a card that effectively duplicated the function 
on an IBM SPP, all that would be needed to take advantage of so many 
parallel I/O devices being dumped daily is appropriate software.

Thus answering the question that prompted this inquiry, "Why can't I use a 
parallel zip drive with my Apple IIe?"

-Greg

> Making the printer port bidirectional came much later.
>
>  Michael
>