Fully wired and working ! New subproject spawned.

A project log for SPAM-1 - 8 Bit CPU

8 Bit CPU in 7400 with full Verilog simulator and toolchain

John LonerganJohn Lonergan 08/01/2021 at 21:300 Comments

I wired in the register file, the RAM, the ALU and the memory address registers 

Did it work?

No, an error showed up when I tried running the CHIP-8 Tetris program.  

I spent hours trying to figure our my mistake and in the end it was my wiring of the signals from a 74245 transceiver being off by one pin. Gah !

Anyway, I happily watched SPAM-1 playing Tetris but without any means to interact with the game and having no random number generator (yet) for CHIP-8 it was a major milestone but limited.

It has been great though that I have had literally zero timing issues with this CPU that didn't also show up in the Verilog simulation - this has been a great vindication.

I have two options for integrating a controller into SPAM-1. The first is to provide the hex keypad input via the over the UART as I've done previously and the other is to wire up some games controllers to the hardware; specifically a pair of Nintendo NES controllers. This latter approach helps wean the CPU off the UART interface and eventually I'll add a VGA interface so the UART inteface can be detached entirely.  

Anyway, to fill in a few of the hardware gaps including the lack of games controllers I've come up with a side project to build a parallel interface adapter to NES controllers.

This new device will also provide a whole load of other peripheral functions and it's rather akin to how the 6522 complements the 6502.

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