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H8/300 Dependent Features


as has no additional command-line options for the Hitachi H8/300 family.


Special Characters

`;' is the line comment character.

`$' can be used instead of a newline to separate statements. Therefore you may not use `$' in symbol names on the H8/300.

Register Names

You can use predefined symbols of the form `rnh' and `rnl' to refer to the H8/300 registers as sixteen 8-bit general-purpose registers. n is a digit from `0' to `7'); for instance, both `r0h' and `r7l' are valid register names.

You can also use the eight predefined symbols `rn' to refer to the H8/300 registers as 16-bit registers (you must use this form for addressing).

On the H8/300H, you can also use the eight predefined symbols `ern' (`er0' ... `er7') to refer to the 32-bit general purpose registers.

The two control registers are called pc (program counter; a 16-bit register, except on the H8/300H where it is 24 bits) and ccr (condition code register; an 8-bit register). r7 is used as the stack pointer, and can also be called sp.

Addressing Modes

as understands the following addressing modes for the H8/300:

Register direct

Register indirect

@(d, rn)
@(d:16, rn)
@(d:24, rn)
Register indirect: 16-bit or 24-bit displacement d from register n. (24-bit displacements are only meaningful on the H8/300H.)

Register indirect with post-increment

Register indirect with pre-decrement

Absolute address aa. (The address size `:24' only makes sense on the H8/300H.)

Immediate data xx. You may specify the `:8', `:16', or `:32' for clarity, if you wish; but as neither requires this nor uses it--the data size required is taken from context.

Memory indirect. You may specify the `:8' for clarity, if you wish; but as neither requires this nor uses it.

Floating Point

The H8/300 family has no hardware floating point, but the .float directive generates IEEE floating-point numbers for compatibility with other development tools.

H8/300 Machine Directives

as has only one machine-dependent directive for the H8/300:

Recognize and emit additional instructions for the H8/300H variant, and also make .int emit 32-bit numbers rather than the usual (16-bit) for the H8/300 family.

On the H8/300 family (including the H8/300H) `.word' directives generate 16-bit numbers.


For detailed information on the H8/300 machine instruction set, see H8/300 Series Programming Manual (Hitachi ADE--602--025). For information specific to the H8/300H, see H8/300H Series Programming Manual (Hitachi).

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.

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