Intel C8755A - 1977

When Intel released the 8755 in 1976 and 8755A in 1977 it provided an easy way to interface the 8080 and the 8085 to other components. It was a 16k (2kx8) EPROM with a pair of latched 8 bit I/O ports.  This greatly reduced system chip counts and complexity of board design. The basic 8755A ran at 3Mhz (the later 8755A-2 ran at 5MHz) which allowed interfacing with the 8085AH with zero wait states. The 8755A continued to be used well into the 1980s with many processors (Intel and others)

Intel D87C75PF - 1988 Engineering Sample

By 1988 the 8755A was out of date, its 16k of EPROM space was insufficient for most designs and its power consumption was much higher then contemporary parts. Intel sought to remedy this with the release of the 87C75.  The 87C75 is essnetially a 27C256 EPROM, and 82C55A port expander, and latches combined on a single chip. It was made on Intel CHMOSII-E process which reduced power consumption (from 1.5Watts to 500mW). It ran at a max of 5MHz and the EPROM was bumped up from 16k to 256k. It was designed to interface direction to the 8051, MCS-96 and i188 processors.

Why then do we find so few examples of the 87C75PF?  The late 80′s and early 90′s also ushered in dozens of microcontrollers and embedded processors that had all of the 87C75′s features on chip; larger EPROM on die, more I/O ports, and the widespread use of Flash on microcontrollers effectively made the 87C75PF obsolete.

Its well known that manufacturers such as Intel and AMD will sell quad cores as dual cores, or 6-cores as quad-cores in order to meet demand, or to use dies that didn’t ‘make the cut.’ This process has been going on for over 30 years though. Back in the 70′s and 80′s it was very common for a device such as this:

Intel D2704 4k EPROM

Which is a 2704 4k EPROM, to actually be made from a 2708 die, just with not all the leads connected, or sometimes, with them connected but just labeled as the smaller part. In a production environment, it is cheaper to have a single production line making dies that can be used in more then one device, then having an entire seperate production line just to make a product that may not be the most popular.  Look at this die shot (its a bit blurry) but you can see its a 2708 die.

2704 with 2708 die

Once again, whats new, really isn’t we have just went from small EPROMs, to CPUs with billions of transistors

Electronic Arrays was born in the late 60′s back in the time of many start-ups (which mostly trace their roots back to Fairchild)  EA attempted to make a CPU called the EA9002, but production problems kept them from going anywhere with it.  They made EPROM’s likely to keep them afloat (and only 8k ones at that).

Electronic Arrays 2708

This EPROM was made in early 1977, less then a year later EA was bought out by NEC, now a world leader in electronics.