For detailed information on the H8/300 machine instruction set, see H8/300 Series Programming Manual. For information specific to the H8/300H, see H8/300H Series Programming Manual (Renesas).
as implements all the standard H8/300 opcodes. No additional
pseudo-instructions are needed on this family.
Four H8/300 instructions (add, cmp, mov,
sub) are defined with variants using the suffixes ‘.b’,
‘.w’, and ‘.l’ to specify the size of a memory operand.
as supports these suffixes, but does not require them;
since one of the operands is always a register, as can
deduce the correct size.
For example, since r0 refers to a 16-bit register,
mov r0,@foo
is equivalent to
mov.w r0,@foo
If you use the size suffixes, as issues a warning when
the suffix and the register size do not match.