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Use of RRC (Rotate right through carry) in Keil

Tom Leys

The 8051 family of microcontrollers has a very useful assembly instruction RRC. This instruction rotates carry into the MSB of the given register, shifts that register right by 1, and carry becomes equal to what used to be the LSB of the register.

  bit NewCarry;
  unsigned char Data;

  NewCarry = Data & 0x01;
  Data = (Data >> 1);
  if (Carry){
    Data = (Data | 0x80);
  }
  Carry = NewCarry;
Basically it does the above, but all in one instruction. I was wondering what the easiest way to include this in my code was. What I want to do is to read a microcontroller pin into carry, shift it into a data byte, and then use the bit that shifts off as an exit condition. Is there an easy way to include a single assembly instruction in Keil? Perhaps a Intrinsic function?

Thanks

-Tom

Parents
  • 0 in reply to Tom Leys

    It seems like a pain to write a full routine in assembly when there is only a single instruction that C cannot provide.

    When you choose to use a "higher level language" you sell your control to the author(s) of that language.

    As K&R did not see a use for "rotate" only "shift" is available in C.

    Keil has added some "keywords" to C which the standard defines as "language extension" but there is (AFAIK) no "allowance" for adding an "instruction".

    If you do not like what C does you MUST go assembler.

    A fact of life - it serves no purpose to complain.

    Erik

Reply
  • 0 in reply to Tom Leys

    It seems like a pain to write a full routine in assembly when there is only a single instruction that C cannot provide.

    When you choose to use a "higher level language" you sell your control to the author(s) of that language.

    As K&R did not see a use for "rotate" only "shift" is available in C.

    Keil has added some "keywords" to C which the standard defines as "language extension" but there is (AFAIK) no "allowance" for adding an "instruction".

    If you do not like what C does you MUST go assembler.

    A fact of life - it serves no purpose to complain.

    Erik

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