6805 to 68h08 conversion

Jun 01, 2006 2 Replies
D

We're looking at converting a PCB from 6805 to 68H08. Freescale (Motorola?) have a document that says the H08 is enhanced "fully object code compatible" version of the 6805. I suspect this just means that the opcodes for e.g. BRA somewhere, are the same in H08. I know most H08 instructions execute faster than 6805..



I will read the manuals in detail to compare but I'm wondering if anyone is aware of any differences in the operation of SPI, SCI, Timers etc where 6805 code will behave differently on the H08 or any problems that might occur migrating from 6805 to H08.



Thanks.


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S

I just ported about 5,000 lines of '05 assy code to '08 code. It mostly works without change. The trickiest work was setting all the new control registers. They are all slightly different and took some tweaking. You also have to be careful with 8-bit and 16-bit instructions and watch your stack.

If you have software timing loops, they have to be adjusted.

Grab a download of Freescales "equate" files and put a value on every register during your initialize routine. It will work just fine.

Steve.

Steven D. Swift, novatech@eskimo.com, http://www.novatech-instr.com NOVATECH INSTRUMENTS, INC. P.O. Box 55997 206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA
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