The 6502 ALU in 7400 Logic

After investigating the 6502, Jeremy and I discovered that this ancient processor was still a complex beast of a machine with lots of constituent components and some quirky ways of implementing some features (like the extensive use of gated registers on the output of each combination logic block). The complexity of the 6502’s ALU means that implementing it entirely in large relays is unrealistic. It would be large, costly and the power requirements would be immense.

7400 logic NAND

7400 logic NAND

Instead, we have decided to do what many other 6502 replica makers have done and construct the processor in 7400 logic first. After searching through the 6502 Microprocessor resource, we found a pretty awesome resource created by a person who seemingly goes by the name of lateblt. He/she has produced a brilliant and in-depth guide to an interpretation of the 6502 using 7400 logic chips. We read through and scrutinised their work to see if we could find any tips for our project, but reading it also gave us a better understanding for how the 6502 works. With this, we’ll be able to construct a functional prototype of the ALU in no time (hopefully). Below is a list of the 7400 chips that we will be using:

7400 Parts List

7400 Parts List

This rapid design process allows us to quickly construct the basic system and get started on the fun stuff – interfacing with the internet, replacing some logic with loud, flashing relays and also using some NIXIE tubes to display the contents of the registers.

NIXIE Tube Clock

NIXIE Tube Clock

So our parts are on order and we hope to get back to you soon about the prototyping stage. We’ll be taking lots of photos and some video so you guys/gals can keep up to date with our progress. We can’t wait to get our grubby little hands on the chips and produce V0.1 of the Twitalu!

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