68764C

[Ludis Langens]

I found a reference that gives the pin out of the Motorola 68764 8K*8 EPROM.
Here it is, along with several other EPROMs of a similar size:

2764  TMS2564       68764          TMS2532  TMS2564  2732     2764

 VPP      VPP      .......                  VCC               VCC
 A12     ~CS1      :     :                  ~CS2              ~PGM
                A7 +--_--+ VCC     VCC      VCC      VCC      NC
                A6 |     | A8
                A5 |     | A9
                A4 |  6  | A12     VPP      A12      A11      A11
                A3 |  8  | ~E/VPP  ~E/~PGM  ~E/~PGM  ~OE/VPP  ~OE
                A2 |  7  | A10
                A1 |  6  | A11     A11      A11      ~CS      ~CS
                A0 |  4  | D7
                D0 |     | D6
                D1 |     | D5
                D2 |     | D4
               GND +-----+ D3

It looks like you can read a 68764 as if it is a TI TMS2564.  Programming it
will be a problem.  None of the standard EPROMs have a (25 volt) programming
voltage (VPP) that gets pulsed for each byte.  You could try building an
adapter socket/circuit that allows it to be programmed as a 2764 or TMS2564.
You'll need a transistor that gates the seperate VPP voltage onto pin 20.

Before you build an adapter to the TMS2564 pinout, make sure your programmer
can handle it.  My programmer doesn't handle any of the TMS25xx series!  I
had to build a 2732 to 2532 adapter just to read some 2532s.

                   unsigned long BinToBCD(unsigned long i) {unsigned long t;
Ludis Langens         return i ? (t = BinToBCD(i >> 1), (t << 1) + (i & 1) + 
ludis at netcom.com                 (t + 858993459 >> 2 & 572662306) * 3) : 0;}