Re: How can clueless seller tell if IIgs is a ROM 3?

[David Wilson <mcs6502@gmail.com>]

On Oct 25, 8:49 pm, demp...@actrix.gen.nz (David Empson) wrote:
> Aren't the EPROMs a greater number of pins? The masked ROMs are 28-pin
> chips, but the logic board has provision for a 32-pin chip, and that
> would be required for a 128KB EPROM (not enough pins to have VPP as well
> as the address pins and CS in 28).

The ROM socket in the original IIgs was designed for a 27512 and then
upgraded to a 1Mbit ROM (I have a photo of a IIgs m/b with a 27512 and
the name of the A16 signal is ROMOE/A16).

The ROM sockets in the 1MB IIgs mother board are designed to take 28
pin 1Mbit ROMs or 32 pin 1Mbit EPROMs (with non-standard pinouts {A16
on pin 24 instead of pin 2 - this is a HN27C301G or a TC571001D
instead of a 27C101/27C010/571000 according to my memory data book}).

P.S. There have been EPROMs with a tri-level /CE/Vpp pin (the MCM68764
for one) so a 1Mbit EPROM in a 28 pin package could have been feasible.