Kansas City Standard (Cassette Tape) Decoder for the 6502 Computer

January 7th, 2023

This is part of a multipart series where we’ll be modifying a homebuilt 6502 processor computer in strange and creative ways.

In this part of the series we’ll be building a circuit to demodulate (or decode) Kansas City Standard audio and load that onto our 6502 computer.

Kansas City Standard or BYTE Standard, was a standard developed by BYTE magazine back in in the late 70’s. It was used to store computer data on standard, low-cost, audio cassette tapes. It was designed to allow common people to be able store data at home as there weren’t many options to do so back around that time. There were even radio shows where they would broadcast out Kansas City Standard formatted audio and nerds like you and I would tune in to, listen to the broadcast and record the last part of the show to “download” a new computer program!

At the conclusion of this KCS build, we’ll be able to load our Ben Eater 6502 from tape!

Part 1:
We’ll go through the history of the Kansas City Standard, some deep level details, and then an overview/theory of how the circuit works. At the end of this video, we’ll have a demodulated UART stream ready to feed into the logic part of the circuit.

We’ll also be introduced to Mr. Monostable, a refined gentleman with a short temper.

If you’re interested in a kit to perform this build yourself. I’ll put one together if there’s enough community interest. (Update: I did!

Part 2:

In this video we latching (or holdon to) the data coming in and we FINALLY get to see some Kansas City Standard data being decoded!

Part 3:

In this video we take the next step in our project and can finally load data from the KCS circuit! We do this by adding an additional W65C22, adding some hardware to handle more interrupts, and update some code.

Part 4: