Delta Island

A brief rundown of the tester's main parts:

Address Bus LEDs
Increment in binary as the CPU executes. After an entire cycle through the Address Bus, any LED which did not illuminate at all can indicate a dead Address Bus line on the CPU.

FCx LEDs
Display the values of the FC lines of the 68000 CPU, which are used to notify external hardware of the type of access being performed on the address bus, e.g. supervisor/user code/data.

Halt Button
Activates the Halt line of the CPU, suspending all function. Upon release, the Address Bus LEDs resume counting from the state in which they were prior to Halt being asserted.

Reset Button
Resets the CPU to its initial state. After release, the Address Bus LEDs once again begin counting upwards from zero.

Frequency Select Switches
Allow the CPU to be driven at a variety of frequencies ranging from 750 kHz to 16 MHz. The 68000 supports changing its input clock on the fly while Halt is asserted. Note: Avoid turning more than one switch to the On position at once.

So, cool! Now I have a tester for all my 68000 CPUs! Well... kinda. Not so fast. oops.png There are a few tweaks which need to be made for the future Revision B board:

Correct the labels for FC0 and FC2; they are currently transposed.
Install current-limiting resistors on all the LEDs. In cases of catastrophic CPU failure such as a severe short, full current could be passed directly through the processor to the LEDs, damaging them.
Replace the switch bank with a rotary switch to prevent multiple clocks from colliding in the event of two switches being set to the On position simultaneously in error.
USB power is sufficient; the ATX connector could be eliminated.
Revision B of this tester will incorporate these changes, feature additional adapters to allow testing of other members of the 68000 family, and will likely be smaller as well. One more thing added to my stack o' projects! rolleyes.png