Motorola MC68705 Projects

Motorola decided to adapt their popular 6800 processor for the embedded market by removing everything that made it functional. I was fortunate enough to find an entire tube of these ceramic waste products during college.

Two registers, 4MHz operating speed, 112 Bytes of RAM, 1804 Bytes of EPROM, and no addressing modes supporting indirection. Sometimes that's all you need.

All code listed on this page will compile in DASM's 68705 mode unless otherwise noted.

Reference Materials
Datasheet Courtesy of Motorola
Programming Module Motorola's official programmer design, which requires manual copying from an EPROM to the MC68705. I suggest just using a generic programmer like a ChipMaster, DataMan, or TopMax to reduce this chip's already large number of inconveniences.
Equates Microcontroller equates, specifically for the xP3 model.



Useless Die Roller
4-15-2011

An extremely over-engineered die roller.

The RGB segments are controlled by a 3-Channel Software PWM Driver with ~6-Bit Per-Channel accuracy (using the 68705's single timer). So you get around 18-Bit color from the RGB LEDs with a ~70Hz refresh.

Because of the PWM driver's memory usage, there was only enough system stack space left for one IRQ and one JSR. Right on the edge...

The display is actually quite stable (unlike in the example video), and aside from the poor mixing in the diodes, ended up looking nice.

Design Materials
Board Schematic A helpful tool for getting rid of these microcontrollers without just throwing them in the trash.
68705P3 Source Written for use with DASM and the 68705P3 equate set above.
68705P3 Binary RAW Binary which can be used with most generic chip programmers.
Video The die performing its only function.



The Worst Clock
1-27-2011

Puts a surprising amount of effort into keeping time.

Design Materials
Board Schematic A helpful tool for getting rid of these microcontrollers without just throwing them in the trash.
68705P3 Source Written for use with DASM and the 68705P3 equate set above.
68705P3 Binary RAW Binary which can be used with most generic chip programmers.
Video The clock performing its only function.


All content by Osman D. Celimli unless otherwise noted.
Not all of said content guaranteed to be useful. Some is probably quite old and dumb.