Quote Originally Posted by dave w View Post
The 1227747 uses a 4K chip. The AT28C64 is a 64K chip just like the 27SF512 is a 64k chip.
Correct me if I'm wrong, but the 1227747 uses a 2732 which is a 4Kx8 (32Kb) chip, the 28C64 is an 8Kx8 (64 Kb) chip, the SF512 is a 64 KB, being a 512Kb chip...I think. The big difference is the B vs the b, bits vs Bytes.

Quote Originally Posted by dave w View Post
Offsets for a 4k chip being programmed into a 64K chip
Microchip AT28C64
Buffer -> 000000 -> 000FFF or Hexadecimal for 4K chip memory size
Address -> 00F000 -> 00FFFF or Hexadecimal addresses to program only the bottom 4K addresses of a 64K chip

For example if you were going to program the AT28C64 for the second generation TBI computer 16197427 which uses a 64K chip no offset is needed.
Buffer -> 000000 -> 00FFFF or Hexadecimal for 64K chip memory size
Address -> 000000 -> 00FFFF or Hexadecimal addresses to program all addresses of a 64K chip

dave w
Today, after spending a few hours figuring out how to use my 30 year old Needhams EMP-20 programmer, I successfully programmed the AT28C64B with buffer offsets 1000-1FFF, which should be the last 4K of the 8Kx8 space, the first 4K being 0000, 0FFF...I think. It's been years since I have done this stuff. I confirmed data in the chip matches the data in the buffer, but just offset to the last 4K of the 28C64. I built the 28P ZIF mod socket and soldered it onto the 747 board today, I won't know for a while if it works, but it should.

Thanks for the help.

Cheers