Monday, March 5, 2012


The Motorola 6809 has a cousin.  Yes, her name is 6309.  Actually the 6309 is a clone of the 6809 and is/was made by Hitachi.  For years, CoCo guys were sticking them in their systems to replace the 6809 because the 6309 is made from a CMOS process and runs cooler and takes up less power.

It took a Japanese guy named Hirotsugu Kakugawa to write a post to the comp.sys.m6809 Usenet newsgroup in 1992 entitled "A Memo on the Secret Features of 6309" to open up the potential of this chip to the CoCo world (see this link for the original message).  It turns out that the chip that a lot of CoCo users were running for years had extra registers, 16 bit multiply and 16/32 bit hardware divide instructions, plus other cool bit manipulation and block copy instructions.  Not only that, but the chip could be put into a mode that would shave 1 cycle off of many instructions.

Soon, intrepid developers began writing software to take advantage of the new-found power of the 6309, including updating Microware's OS-9 operating system (where NitrOS-9 got its name).  Performance was improved greatly and it set new speed records for the CoCo.

You would expect that the 6309 would also work in the Liber809, and that was the plan, but for a few weeks now, I was aware of a problem.  The 6309 wouldn't work in the Liber809 board, neither the Frankenproto wire beast that I handmade, nor the prototypes that came in last week.  The 6809 ran fine, but the 6309 would just lock up the machine.

It turns out that gate delays caused a glitch in the E and Q clocks.  Gary noted this in one of the logic analyzer shots I sent over to him, and surmised that switching two pins on the 7400 would cause the signal to arrive two gate delays earlier and eliminate the clock spike.  Today for lunch I quickly rewired the prototype and tried the 6309, and sure enough it came up.  So now the Liber809 also works with the 6309.

Speaking of prototypes, both have been sold and are getting into the hands of their new owners as we speak.  Some additional testing on their end will solidify things and we'll soon move to a larger run of boards that are optimized for both part count and space.

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