Subject:
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RE: H8 & unaligned word accesses
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 11 May 1999 14:20:32 GMT
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Viewed:
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772 times
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Matt wrote:
> I discovered an interesting "feature" of the H8 series processors used in
> the RCX. It will only affect people using raw H8 code on the RCX, such as
> those of us using LegOS, and perhaps pbforth.
>
> The H8 does not support unaligned word accesses. If you do a word (16-bit)
> access to an unaligned address, the processor actually accesses the previous
> address! This is documented in the H8/300 programming manual (on page 4,
> just above figure 1-2).
Right you are Matt. This created a bit of trouble when I was porting the original
pbFORTH code over to the H8. I THINK this is because the H8 core is extensible
to a full 16 bit machine - or even 32. The "8" in H8 is a misnomer except at
the bottom end of the family where we are, of course, stuck.
It's one of those "heads up" bits of info that can turn on a light when debugging
wierdness. Ill chack out the behaviour of pbFORTH doing unaligned word accesses
in interactive mode...
Cheers,
Ralph Hempel - P.Eng
--------------------------------------------------------
Check out pbFORTH for LEGO Mindstorms at:
<http://www.bmts.com/~rhempel/lego/pbFORTH/default.html>
--------------------------------------------------------
Reply to: rhempel at bmts dot com
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Message has 1 Reply:
 | | RE: H8 & unaligned word accesses
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| (...) I am currently using the H8S/2144 processor at work. The above statement is totally correct - the H8 series is directly compatible with the 16-bit H8S series. Because the H8S is a true 16 bit processor, internal memory is always accessed as a (...) (25 years ago, 11-May-99, to lugnet.robotics)
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Message is in Reply To:
| | H8 & unaligned word accesses
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| I discovered an interesting "feature" of the H8 series processors used in the RCX. It will only affect people using raw H8 code on the RCX, such as those of us using LegOS, and perhaps pbforth. The H8 does not support unaligned word accesses. If you (...) (25 years ago, 11-May-99, to lugnet.robotics)
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