Re: Do it yourself upgrade: IIgs ROM 01?

[dempson@actrix.gen.nz (David Empson)]

O Aaland <oaaland@aol.com> wrote:

> My EPROM burner lists an Intel EPROM that is 1MB in a 128 pin 
> configuration. Without looking it up I believe the number was 
> 27C010. They also list another that is 1MB in a 32 pin configuration.
> The number of that one is, I believe, 27C011. Would the 28 pin EPROM 
> work as a IIGS ROM 01 chip?

I'd have to see the pinout to comment on that.  I doubt the part number
is 27C010, as that is the number which Atmel use for their 32-pin 1mbit
(128Kx8) EPROM.  (Matching numbers from different manufacturers tend to
mean matching pinouts, but this isn't always the case.)

I was not aware of any 28-pin 128Kx8 EPROMs.  To do this, the chip needs
27 pins just for power, ground, address (17) and data (8).  This leaves
one pin for some combination of Vpp, chip select and output enable,
which limits the usability of the chip and would complicate the
programming algorithm.

I suspect it is a rare part that is intended to be used for prototyping
prior to masked ROMs being used, while the 32-pin chip is the normal
part for permanent use as an EPROM.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand