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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).
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.