The Expansionport Sniffer is a small circuit board that is plugged between the expansion port of the C64 and an expansion port cartridge. The board shows the activity of the control signals on the expansion port via a row of LEDs while the C64 is accessing it. The display delay can be changed to make high frequency signals more visible.

The 15 signals monitored are:
RESET, IRQ, NMI, RW, EXROM, GAME, ROML, ROMH, DMA, PHI2, IO1, IO2, BA, DOT-CLOCK, +5V

To keep the design as simple as possible, the monitoring and LED control is done by an Arduino Nano.
Last Update: 25.02.2021
Expansionport Sniffer
Expansionport Sniffer Prototype
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