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From: "D Poinsett"
Subject: Re: To C or not to C
Date: Sun, 5 Jan 2003 12:58:22 -0500
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Good question. You are right; it's still read-modify-write. But in the
HC11/H12 there are machine instructions that do this all in one instruction
cycle thus interrupts or other hardware-sourced changes are locked out until
the instruction completes. This is in contrast to read-modify-write routines
where each operation is performed with separate instructions. Sorry I was
not more clear.
"Frank Bemelman" wrote in message
> "D Poinsett" schreef in bericht
> > Hi Nico,
> > Good point.
> > However, bit twiddling/testing macros vary depending on the target
> > and the way the macro is written. A common method is to read a byte,
> > some AND or OR instruction, and possibly write the result back. For
> > processors like the HC11/HC12, multiple bits can be set/reset/tested in
> > instruction eliminating the possibility that changes may have occurred
> > that register/memory location (due to an interrupt or hardware, for
> > example), changes that could be disturbed if the result of the macro bit
> > twiddling/testing is written back to that location after the change
> > occurred.
> Also for memory locations? How can that work other than
> a read-modify-write scheme?
> Frank Bemelman
> (remove 'x' & .invalid when sending email)
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