UNILAB three-chip-plus-clone

A clone of the main UNILAB 6502 learning board, part number 540.300

Features & changes over the original UNILAB educational system:

• Compatible with 6502/6522 or newer 65C02/65C22 fully static parts
• 1Mhz crystal replaced with oscillator module (more readily available)
• Internal/external clock selectable by jumper
• Address bus, Data bus, R/W and Clock available on headers to be compatible with Ben Eater's Arduino Mega Moitor
• Compatible with original three-chip-plus I/O peripheral boards, Program Memory Board, and Program Loader
• Original PCB form factor (yes, rather large by today's standards but I went for originality
• See note at bottom of this page for ISS1 (ONLY ISS1) board error and modification

Assembled PCB (ISS1):

Schematic (ISS2):

ERROR and correction for ISS1 schematic and PCB

Note: there are two errors on the ISS1 ONLY schematic and boards, these are fixed on ISS2 in the design:

1. Polarity of POWER IN is reversed on the PCB legend (but correctly diode-protected)
2. Clock error, where U4 (the 6522 pin 25) should be driven with PHI2 (same phase as U5, the 6502) and U2 pins 2,10,12 should be driven with ~PHI2 (inverted phase compared to the 6502 and 6522). Correcting this involves two track breaks and two wires being fitted to the PCB as below (one on the component-side below the socket of U3, one on the solder-side):