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A project log for 8 Bit Breadboard CPU

A home-brew 8 bit Microprocessor built on a breadboard 64K Address Space, IRQ, and DMA 16 Bit Stack Pointer, 4 8 bit Registers or 2 16 bit

2-Zons2-Zons 01/06/2019 at 00:183 Comments

Finally received the delivery I was waiting for to start building something.  This is the clock circuit.  It's pretty much an exact copy of Ben Eater's 8 bit computer clock.  Starting from the left: A 555 circuit to generate and adjustable square wave clock that can run as slow as 0.5 Hz.  Second, another 555 circuit to debounce a pulse that will be fed into the output logic for single stepping.  Third, a final 555 circuit to debounce the enable circuit that feeds into the output logic to select from the single step or clock.  Red button is single step pulse, beside the toggle for the select.  Next are two quad nand 7437 for the output logic.  Second chip is not used yet.  Will be used to generate inverse clock, and halt for DMA.

No need to comment on the crappy soldering job on my power input.


Amos wrote 01/06/2019 at 03:49 point

Nicely done. I like the use of the NAND gates instead of ANDs Ors and NOTs which Ben used. I am sticking with Ben's clock design while I build my first prototype, but I am looking at another, simpler, clock circuit for my next revision - I think his design is great for teaching the concepts, but it is definitely overkill.

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2-Zons wrote 01/06/2019 at 21:45 point

I will be using this clock for initial testing.  Once I've got the whole design working I will be replacing it with a much faster clock. I want to see how fast I can get it running without errors.  That's the plan anyway.

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Amos wrote 01/07/2019 at 00:44 point

Good luck with the project - I can't wait to see where you take this.

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