3. Writeable Control Store
 

Hardware: DIY ISA bus interface logic

Software: MS DOS debug.exe

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With the advent of microprocessors and later microcontrollers, the memory chip market expanded to provide read only memory chips for programs but when they first appeared, programmers for these chips were expensive. My favourite microcontroller was the Intel 8031, the ROMless version of the 8051. There was also the 8751 with on-board programmable EPROM, but these were also prohibitively expensive. After a while EPROMs expanded to EEPROMs (aka EAPROMs) which were the predecessors to today's Flash memory chips. When EEProms appeared, I devised a very crude memory chip programmer which consisted of a prototype ISA board with a socket for an EEPROM that could be programmed simply by using the debugger that came in DOS, by initiating a memory copy command. I christened this my Writeable Control Store, and it was this method I used for many years to program code into chips, such as for the LF frequency generator and the automative dashboard project, until eventually the Microchip PIC series came out and I started using their USB based programmers.

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