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

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

"mdj" <mdj.mdj@gmail.com> wrote in message 
1166607129.131341.260290@t46g2000cwa.googlegroups.com">news:1166607129.131341.260290@t46g2000cwa.googlegroups.com...
>
> Michael J. Mahon wrote:
>
>> > The 16bit units can surely handle the job, but then you're dealing with
>> > QFP's and .5mm lead spacing which is a bit hobbyist unfriendly, but
>> > still quite affordable.
>>
>> It depends on what you think the pixel rate is and how much
>> computation the microcontroller is doing for each one.  It's
>> hard to do any stimulus/response action without taking a few
>> instructions per pixel.  Pretty soon, you're in >80MHz territory
>> for the microcontroller!  I just heard the "cheap" and most of
>> the "simple" falling off the table...  ;-)
>
> Well, in terms of converting the digital RGB signal from an existing
> RGB adapter to analog (with colour correction) a 40 MIP PIC should do
> the job. These are around $5-$10, but as noted are in inconvenient
> packaging.
>
> You'd still need to add op-amps to buffer the analog output.
>
>> Actually, a very fine conversion could be done with a shift
>> register for the video bits running at 14MHz (easy) and then
>> using 12 bits (parallel out) from the shift register to address
>> a couple of fast SRAMs (or one if wide) to get at least 12
>> and as many as 15/16 bits out per 14MHz cycle.
>>
>> These bits would go to D/A converters (or resistors) whose
>> output would be buffered by video op amps to drive 75 Ohm
>> RGB monitor loads.  (Of course, sync from the Apple would
>> need to be added appropriately.)
>>
>> The SRAM(s) would have to have logic around them to allow
>> them to be loaded at "boot" time with the desired color
>> table that could easily handle:
>>
>> 1) a beautiful NTSC composite simulation,
>> 2) a sharp RGB rendering,
>> 3) whatever other mode(s) you find interesting.
>
> Sure you could do that, but that's a different problem - creating a new
> RGB adapter from scratch vs modify the output of an existing one.
>
> Of course the approach you outline could be used for the original case
> as well, but wouldn't fit convenentily into a cable like my resistor
> solution does now - too many parts.

    Do you know if there is another way to use Apple IIgs' 16 Color table 
without using ROM or EPROM chip?  It is like using boolean logic.  I do know 
GAL16V8 chip is only the way to go.  I have GAL16V8 chip from RGBI port of 
Apple //e's RGB card to CGA digital monitor.  GAL16V8 chip is used to swap 
16 CGA colors.  GAL16V8 chip is perfect for 14MHz clock cycle signal.
    Do you agree that GAL16V8 chip is only the solution for Apple IIgs' 16 
color table.

Bryan Parkoff