Register Names
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   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).

   The two control registers are called `pc' (program counter; a 16-bit
register) and `ccr' (condition code register; an 8-bit register).
`r7' is used as the stack pointer, and can also be called `sp'.