Den Tue, 7 Nov 2017 19:19:44 +0000 (UTC) skrev Steve Gray <sjgray@rogers.com>: > Nope, that's about it. You could probably wire it up in an hour. Me, > it takes years ;-)Basically, the circuit that handles the current > monochrome 80 columns is duplicated for colour. Due to the 1Mhz clock > commodore had to split the ram into two, read them at the same time, > latch them and shift them out one after the other. So for an > 80-column colour screen you'd effectively have a 32-bit wide video > buss. The article mentions a 160x100 pixel "graphics" mode, which I > assume is just done with standard petscii block characters. Steve It's interesting that the 8296 has two banks of 64k, but has the data bus in parallell and reads two bytes for the graphics between each cpu memory access. An 8296, or atleast a replica using about the same hardware, could do 80 columns in color if the memory would be split so those two reads per 1MHz half cycle would read 16 bits each, 8 bits from each memory bank. On a real 8296 that would require both an additional LS245 together with lifting the DO/DI pins on each RAM chip in one of the banks, and also making some logic that rearranges what part of physical memory maps to where in the CPU memory map (i.e. as the machine has 128K, where 96K is officially to be compatible with 8096 and 32K is just used for display memory and configurable to appear in the space that's usually used for expansion ROM's, leaving quite a bit of memory unusable. That part of memory should be remapped so it is in the lower part of one of the "96k" banks, and the lower part of that "96k bank" that's then leftover should be used as attribute ram. Somehow. Perhaps. Or as a first stage just use one of the "96k banks" as attribute memory and have an i/o port making it possible to turn on and off the attribute feature. P.S. while I'm at it, it might be worth looking at current SRAM prices before designing a new "B" type motherboard using SRAM's. I don't know how much the price is for the slower devices that's adequate for this kind of project, but I've read that the faster SRAM's used in the open source Amiga accelerator Terribe Fire TF530 (see the forum EAB) is much higher today than at the time the design were made just a short while ago. -- (\_/) Copy the bunny to your mails to help (O.o) him achieve world domination. (> <) Come join the dark side. /_|_\ We have cookies. Message was sent through the cbm-hackers mailing listReceived on 2017-11-08 16:00:03
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