On 2006-07-03, Lichen Wang <[email protected]> wrote:
> P1IN is a hardware read-only 8-bit Special Function Register
> (SFR). Every time you read it, it gives a potentially
> different result. In addition, it may result in some side
> effect in the hardware.
>
> Suppose I want to read P1IN twice and I do not care about the reading and
> only want to cause the hardware side effect twice. In Assembly, I would write:
> mov.b &P1IN,Rx
> mov.b &P1IN,Rx
> where Rx is one of the un-used registers R4-R15.
>
> How do I do the same thing in C?
(void)P1IN;
(void)P1IN;
> (P1IN is declared to be a volatile unsigned char in the header file.)
> Can I write two = P1IN + P1N;?
Yes.
> How about if (P1IN + P1IN) {/* nothing */}?
Sure.
> I am just starting to use c as a tool to generate code for
> embedded system. I understand and accept the fact that in
> order to be able to use any tool, you have to learn how to
> use that tool first. But is this like priesthood? Do I have
> to recite in Latin?
No, just PDP-11 assembly language.
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