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A project log for Yet Another m68k Homebrew

A Motorola 68k homebrew on breadboard, this time with a 68010 running at 8MHz

Ross BamfordRoss Bamford 06/09/2019 at 21:441 Comment

After a trying weekend working on the m68k build (see the previous two logs for details) I finally reached the "Hello, World" stage in the board's development. That's right, the UART is now working and integrated with the USB to TTL converter I'm using at the moment.

Once I'd worked out how to get the UART properly initialised, I hooked up the analyzer to the TCLK and SO lines of the 68901 and ran a simple bit of code that would just output "Ok". Here's the trace from that:

The "Ok" characters were moved into the UART data register as immediates. Expanding this to support sending out a null-terminated message exposed a wiring mistake in the board - it was the first time I'd done byte-sized reads from ROM space and it turned out I'd wired the chip selects backwards to the address decoder. With that fixed, I was able to output characters from a constant string in a loop:

Finally, by hooking up the USB converter and plugging it in (to my Windows laptop as the cable is too short to reach my main machine), I was able to verify the results in a terminal:

And just like that, the rosco_m68k now has a way to do output. The challenges and annoyances of the weekend are forgiven - onward and upward!

Discussions

Ken Yap wrote 06/10/2019 at 00:08 point

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