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A project log for SPAM-1 - 8 Bit CPU

8 Bit CPU in 7400 with full Verilog simulator and toolchain

John LonerganJohn Lonergan 07/06/2021 at 01:490 Comments

So I've also wired in the Register file now which means I have a total memory of 4 bytes.

Not a lot but plenty to adapt my trivial UART program to echo back whatever is typed at the console.

This all seems to work fine at around 2MHz which is where my 555 timer clock maxes out. I'm quite interested to see how fast this thing can be made to run on a breadboard. I'm pretty sure that the critical timing data path is about 200ns half cycle, so I'll see if I can get 5MHz at least from it. The single biggest component in the latency is the 80ns-100ns EEPROM used for the ALU, add to that say another 100ns for other components in th data path and 4-5MHz seems reasonable. It will be interesting to see if the IC's outperform the advertised timings.

I've also wired up all the ALU status register flags to the control logic so all that's left to hook up is the Memory Address Registers and the 64KB RAM.

As soon as I have the RAM in place I'll try running some of my MUST more complicated CHIP-8 programs on SPAM-1 CHIP-8 emulator.

This is a massive achievement for me given I've spent ages building this thing in fits and starts.

I'll need to add a few more things like a random number generator and an IO port to which  can add something like a games controller. And, the thing I'm really interested in is adding some video RAM and VGA output.

Anyway lots to come - but I want to get that CHIP-8 stuff working this week if possible.  

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