Freerunning Toshiba TMP68HC000P-16 on a Breadboard

Building my own computer was always a dream of mine. I decided to take the first step by buying a Japanese Motorola 68000 clone, the Toshiba TMP68HC000P-16. Rated at 16 MHz and using CMOS technology, this seemed like one of the best versions of the 68000.

To start with, I tried to freerun the chip. Freerunning is where you hardwire the data lines so that the CPU continually executes the same instruction over an over while the program counter counts up through memory. For the 68000, connecting all the data lines to ground is a common way to freerun the CPU, making it execute OR instructions endlessly.

In the video, I connected all the data lines to ground and all the address lines to LEDs. The interrupt/error related signals are also connected so as not to disrupt the CPU. The clock is an 8 MHz crystal oscillator (should be easier to debug with my cheap logic analyzer at this speed) and there is a reset button connected as well. You can see the LEDs count up as the program counter is incremented.

I ordered some SRAM, EEPROMs, and a CPLD for the glue logic. Though I don't have much free time to work on this project, hopefully I'll have more updates in the future.