On Wed, 2011-08-10 at 20:55 +0200, Bodo Wenzel wrote:
> Hi Mike,
>
> > I am trying to access a sfr with a pointer (mcs51 P2, P2MDOUT, ...)
> It's not a question of the compiler. It is not possible because of the
> opcodes of the MCS51. There is no machine instruction to access SFR
> through a pointer.
Ok Thanks. I've start down the switch statement path. I was just
hoping there was a more elegant solution.
>
> The only solution I once found was to write a function that takes the
> address as argument. In the implementation is a huge switch which does
> the actual access, like this:
>
> __sfr __at (0x80) SFR_80;
> __sfr __at (0x81) SFR_81;
> /* ... be hard-working ... */
> __sfr __at (0xFF) SFR_FF;
>
> unsigned char readSFR(unsigned char address) {
> switch (address) {
> case 0x80:
> return SFR_80;
> case 0x81:
> return SFR_81;
> /* ... be hard-working ... */
> case 0xFF:
> return SFR_FF;
> default:
> return 0; /* or read the internal RAM */
> }
> }
>
> It's a lot of source code but the object code is quite small. To write
> to an arbitrary SFR a similar second function can be written.
>
> HTH
> Bodo
>
>
>
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