[Coco] MPROM woes (cured)

[Phill Harvey-Smith]

Darren A wrote:
> I have a 27512 EPROM in my FD-502 disk controller. It works great so
> long as you program the code into the upper end of the device. This is
> due to the fact that the 502 connects +5V to the extra address pins
> used by the 27512. No wiring adapter is needed.

Indeed, A similar trick I uded for developing CoCo/Dragon software 
(before I started to use flashrom anyway :)) was to make an adapter that 
  had a 3 pin jumper on A14 and A15, with the middle pin connected to 
the rom addressl line, and either end connected to +5V and GND respectivly.

That way I could program the first version of my code to the bottom 16K, 
  and select the jumpers both for ground, then if that didn't work, 
program the next version into the next 16K block, change the jumpers as 
needed and test again.

That meant I could do 4 test cycles per erasure of the EPROM. Also this 
means that you could say program 4 different blocks of code into each 
16K block of rom, and then select the one you want with the jumpers, 
alternate versions of DOS spring to mind here.

> Getting the MPROM to program a 27512 may be a more challenging (if not
> impossible) endeavor.

Indeed, this would probably depend on how simular the programming 
algorithims are, also I suppose that the 27512, uses the pins smaller 
EPROMS use for programming as Address lines, it may be doable, but as 
you say challenging.

Cheers,

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.