When using the 28C256 chip with a stock logic module ... this is
specifically one that has NOT been converted to being in circuit
flashable ...
you MUST enable the SDP(or software data protection) with the eeprom
burner after burning the chip. The address / OE / CE decoding on the
logic module cause problems with writes to the a/d convertor or
something else to put the chip into program mode and either make a big
delay at startup OR corrupt the data.
I fought this for a while when first using 28C256 chips about 6 years
ago. It took me many burns to figure it out. I ended up comparing the
image to what I burnt, putting it in the LM, powering it up, then
reverifying it and finding it changed after powerup.
I know for a fact you can use 2 28C258 chips on stock dual eprom boards
and I do believe you can with the single eprom board also. This is
providing you burn the image at the upper end of the chip as unused
address lines are tied to Vcc.
Any speed 28C256 you can buy these days should work. The 200nS work
with a 2 Mhz muxed 6811, so they are more than fast enough for a 1 Mhz
muxed 6803.