Re: Intel 4004 -50th Birthday (Was 15th Nov 2021)
Attached very untidy schematic of my toggle switch programmed 4040.
Operation is similar to scrumpi, the processor generates the address and the toggle switches can write data to ram.
One of the challenges was the mix of voltages for the different technology.
Display was driven as multiplexed array of LEDs from the 4040 bus, there was quite a lot of ghosting due to very slow logic of the 4040 chip set, but I was able to adjust the timing to get it useable.
As the 4040 is 4 bit data, 8 bit code, and I used bytewide RAM instead of 5101/2101 type, so I used a bus hold circuit to allow updates of 4 bits of code without changing the other 4 bits.
4040 supports two 4K pages of code, intended to use two of 4289 memory interface, but instead I added extra logic to select the two pages of the 6264.
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