Tony,
An ATMEL AT28C64 EEPROM has a READY / BUSY* on Pin1 which would normally go
to an Interrupt.
Best regards, Steven
On Sun, Nov 7, 2010 at 2:09 AM, ard at p850ug1.demon.co.uk <
ard at p850ug1.demon.co.uk> wrote:
  The device [1] that's currently all over my bench
has an empty 28 pin DIL
 socket on one of the PCBs. It's alongside a 27C256 EPROM and 43256 RAM, and
 has a similar pinout.
 In fact the pinout is the standard JEDEC one for 28 pin memory devices
 (with
 A13 on pin 26, WE on pin 27, OE on pin 22, etc) with one exception. Pin 1
 is
 not A14, it appears to be an output, linked to an interrupt pin on the
 80C85
 that links to the aforementioned memory devices and this socket). Oh, and
 to
 an input port pin.
 Any ideas? My first thoughts were an E2PROM or simular, with a ready output
 on
 pin 1, or a RTC/memory device with an interrupt output on pin 1, but I
 can't
 find any obviuos candidates.
 [1] A telephone network simulator. OK, it's not a classic computer, but I
 will
 be using it to test and demonstrate classic computer modems, it's well over
 10
 years old, and contains 6 microprocessors...
 -tony
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