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Two Chip 1806 Circuit

September 25, 2017

I’ve been using Lee Hart’s Membership Card CPU board as the basis for the 1802 Olduino.  It’s great and has a lot of capability and excellent build quality and documentation. As I work toward my high speed 1806 version though, there’s a lot of stuff on the board that I don’t need to drag along – the clock gate chip, the multiple memory types, provision for load mode etc.

As a beginning here’s my two chip 1806 circuit on a breadboard.  I’m using a non-volatile RAM that I programmed using an olduino so I don’t need load mode or a ROM.  I’m not using the upper address bits at the moment so no latch. I’ll next add the address latch and then gating to stop random writes to low memory.

17-09-25 twochip2

UPDATE: I am not getting a solid power on reset with that circuit. I occasionally get a glitch on /CLEAR. It seems there’s major hysteresis in the circuit.  /Clear takes 20 ms to go high with +V but >200ms to go low when +V goes away.  If power comes back within that 200ms it glitches.


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