11-05-2022, 12:10 AM
(10-05-2022, 11:17 PM)mjelic Wrote: OK, so both the basic ROM and the Boot ROM are 128k jobs?? Holy mackerel that's a LOT of ROM to use up!! Aren't those things normally 8K or such?No they are not both 128k.
I'm liking this bank switch idea, along with EDASM in there somewhere.
The Boot ROM is 64kbit or if you like 8KByte & Basic is normally 2x 64kbit or 2x 8KByte ROM's but can be burnt into one 128k (16KByte) to fit here.
So to make the bank switching work you would need to use a 256kbit (32KByte) ROM and switch between the upper and lower 128kbit (16KByte) halves with A14.
As the Boot ROM is only 64kbit (8KByte) you would leave the second half of the lower 128k empty then into the upper 128kbit (16KByte) you would place the two 64kbit (8KByte) ROM images into there.
Switching between Boot ROM and ROM Basic would be a case of changing pin 27 (A14) between a logic low and a logic High.
EDASM (if you like) will be in ROM2 position and would be ignored when booting with the normal Boot ROM. You may even be able to put TELCOM into ROM 3 but that is something I have not tried myself, as all my MB8342 Coreboards have my 512k MOD fitted, which encroaches over the ROM 3 location.
Ernest