[Gmecm] MEMCAL programming

[Jon Dods]

Hi,

Most likely the chips in the Memcals without the window in the top are PROM's not EPROM's or EEPROM's.
Once PROM's are programmed they cannot be erased.

There are a number of PROM's and EPROM's which are functionally and pin for pin the same once programmed.
I'm not aware of any EEPROM's that also fall into this category.
The only thing you need to be aware of is the access speed of the chip, this is usually stated on the end of the part number.
Eg; 27C256-200, 200 being the speed.  A replacement chip must have an equal or faster access time (lower number).

There is also a slim chance that these chips without windows are PLA's, (Programmable Logic Array's).
These can be programmed in a fashion where they will emulate the code in an EPROM but cannot be read back, so it stops people 'stealing' the code in after market Memcals.

PROM - Programmable Read Only Memory
EPROM - Erasable Programmable Read Only Memory
EEPROM - Electrically Erasable Programmable Read Only Memory
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