Re: UDC short mystery - 2 different cards that both hate my Apple 5 1/4" - Different revs?

[David Wilson <mcs6502@gmail.com>]

On Jun 12, 10:58 am, "atfphotogra...@gmail.com"
<atfphotogra...@gmail.com> wrote:
> Sweet! I'll take a look at the these. How do you actually determine
> which eprom you use in each situation? I have a Liron card here that I
> would love to dump the ROM and create another one. Do you count pins
> (24 in this case) and then someone figure out how much memory is on
> the original ROM itself?

You read the part number on the chip (easy if it is an EPROM like the
UDC and not covered in a large label).

The SSC uses a 2716 with the same 256 bytes mapped into the slot CnXX
space. Newer cards like the 1MB Apple "Slinky" Memory card use a 2732
which allows them to have a unique copy of code for each slot.

24pin
2716 = 16 kbit = 2 kbyte
2732 = 32 kbit = 4 kbyte
28pin
2764 = 64 kbit = 8 kbyte (your green UDC has the CMOS version of this:
27C64)
27128 = 128 kbit = 16 kbyte
27256 = 256 kbit = 32 kbyte
27512 = 512 kbit = 64 kbyte

If the card has a mask ROM then I tend to tell the programmer that it
is the largest part with that many pins. Then I look at the contents
and look for either 1/2 or 1/4 all being FF (which tells me that some
of the address pins are actually chip selects) or if the dump repeats
then some pins may be don't cares.