Re: Apple //e's RGB Card To Apple IIgs' RGB Monitor

["Bryan Parkoff" <nospam@nospam.com>]

"Michael J. Mahon" <mjmahon@aol.com> wrote in message 
UeudnUL6c7t8KxXYnZ2dnUVZ_t2tnZ2d@comcast.com">news:UeudnUL6c7t8KxXYnZ2dnUVZ_t2tnZ2d@comcast.com...
> mdj wrote:
>> Bryan Parkoff wrote:
>>
>>
>>>    Please try to answer my one question.  Do you think it is worth to 
>>> use
>>>GAL16V8 chip or ROM chip so Apple //e's RGBI port can be translated to 
>>>Apple
>>>IIgs' 16 colors using 12 bit look-up table in the GAL or ROM chip.  Then 
>>>D/A
>>>chip or resistor network will give correct 16 colors (not 16 CGA colors).
>>
>>
>> Either approach will work just fine, Bryan, which one is 'better'
>> probably depends on what you've got in your electronics workshop.
>>
>> I personally don't like the GAL approach, since that technology is
>> quite old and programmers don't seem to be easily available. It would
>> make it difficult for others to construct the circuit if they wanted
>> to.
>>
>> Using ROMs is also workable, assuming you've got a ROM programmer
>> hanging around. It's probably simplest to use multiple ROMs, but you
>> could get away with one ROM and pair it up with an 8 bit latch.
>>
>> My preferred approach is to use an 8-bit microcontroller, since these
>> are available everywhere, programmers are plentiful, and there's
>> software for every platform to program the things. You'd also end up
>> with a single-chip solution, which by my sense of hardware aesthetic is
>> the most 'elegant' design.
>>
>> Others might consider that using 21st century to solve a 1980's
>> engineering problem is cheating - but you're building it, you get to
>> decide. Just pick an approach, run with it, and let us know how it
>> works out.
>
> The problem is speed.  The video needs to be translated at 3.58
> megapixels per second (if you assume the 140 horizontal pixel model)
> or even faster if you want higher resolution.  14MHz would be my choice
> with a shift register running at the same rate.
>
> Most ROMs and microcontrollers are out of gas at those rates.

Michael,

    I believe RGBI port from Apple //e's RGB card has 14MHz signal.  It 
should work with any ROM chip as clock cycle signal.  How do you say that it 
is out of rate?  I can't imagine that ROM chip might be too fast for 14MHz 
to handle.

Bryan Parkoff