assemblystm8

STM8SF103 Assembly - Load immediate value to ram register

I am trying to write a program in assembly language for the stm8sf103 microcontroller. I would like to store an immediate hexadecimal value in a ram register (such as $0), but this isn't working and i am wondering why:

stm8/
    segment 'rom'

loop
    ld  $0,#5
    jp  loop

    end

I get the error:

as1 : Error 54: Can't match Addressing mode ' ld $0,#5'

Solution

  • Use

    MOV $0, #5

    The instruction doesn't affect any condition flag.

    From the ST8 Programming Manual, the description of MOV is

    Moves a byte of data from a source address to a destination address. Data is examined as it is moved1. The accumulator is not affected.

    There are 3 addressing modes for the MOV instruction:

    • An immediate byte to a direct memory location
    • A direct memory location to another direct memory location (from $00 to $FF)
    • A direct memory location to another direct memory location (from $0000 to $FFFF)

    You can refer to that manual for the supported addressing modes (20 in total), so you can understand why ld $0,#5 cannot work (there is no Direct with Immediate addressing).

    1 I can't understand this phrase, I believe there is a typo (it should be Data is not examined ...). The manual clearly states that no flag is affected.