Quote:
Originally Posted by SiriusHardware
Thanks for pointing out the little problem with NRDS /OE, I probably would have overlooked that.
If I did set about programming a PROM as the address decoder would it be worth trying to map the 'lost' 0.5K somewhere else? I don't think there are any other handy 'holes' in the memory map to drop RAM into, are there - if there were, nobody would go to all the trouble to free up 0200-07FF, they'd just use a hole that was already there?
The PROM isn't the only thing which originally has images but I think some of the original software may depend on the the images existing so that it can reach into two areas with a pointer placed on the boundary.
Despite that, I think forum user 'circuitryboy' did go the extra mile and added mods to remove the other images as well so that RAM could be mapped into those areas.
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Technically yes, the difficulty is in disabling the unwanted images really. It would probably be better to create a PROM to decode for all the devices and remap the top 4 address lines. You could possibly do this by pulling the TTL that does the decode and jumpering in the PROM? But it sounds like a new spin of the board to me!
On my ROM RAM.buffer board I was thinking about I was thinking about using a GAL for the same thing, that is complicated by needing to control the direction of the buffers while NENIN is low.