6502 Clock – A Blast from my past

This is not a PIC micro related post, nevertheless I think it is interesting.

This was a clock I built around 1985/86 using a 6502 microprocessor. It was the precursor to the ‘Record Time Clocks‘ I went on to build using an Intel 8748 microcontroller and eventually the PIC microcontroller based ‘Record Clock Redux‘ project.

The code was written in machine code – I didn’t have an assembler so I wrote the code by hand on paper – entered the HEX opcodes and used a disassembler to check branches and jumps went were I intended. I could work out relative branch offsets in my head at the time. I also knew most of the opcode HEX values from the top of my head. To this day I know that $4C is JMP absolute, $A9 is LDA immediate, $EA is NOP.

It still works, so the EPROM has not given up its data in 36 years. The EPROM programmer was something I built myself and again wrote the code to control it.

Back when this was built sourcing parts and components involved a printed paper catalogue, a hand written order form posted to the supplier, or by 1986 perhaps a phone call followed by a wait for the order to be delivered, and generally no next-day shipping either. Also I was young and didn’t have a lot of money so parts tended to get robbed from one project to build the next.