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2.4.2 General Registers
The H8/300H CPU has eight 32-bit general registers. These general registers are all functionally
alike and can be used without distinction between data registers and address registers. When a
general register is used as a data register, it can be accessed as a 32-bit, 16-bit, or 8-bit register.
When the general registers are used as 32-bit registers or as address registers, they are designated
by the letters ER (ER0 to ER7).
The ER registers divide into 16-bit general registers designated by the letters E (E0 to E7) and R
(R0 to R7). These registers are functionally equivalent, providing a maximum sixteen 16-bit
registers. The E registers (E0 to E7) are also referred to as extended registers.
The R registers divide into 8-bit general registers designated by the letters RH (R0H to R7H) and
RL (R0L to R7L). These registers are functionally equivalent, providing a maximum sixteen 8-bit
registers.
Figure 2.4 illustrates the usage of the general registers. The usage of each register can be selected
independently.
• Address registers
• 32-bit registers
ER registers
ER0 to ER7
General register ER7 has the function of stack pointer (SP) in addition to its general-register
function, and is used implicitly in exception handling and subroutine calls. Figure 2.5 shows the
stack.
• 16-bit registers
E registers
(extended registers)
E0 to E7
R registers
R0 to R7
Figure 2.4 Usage of General Registers
• 8-bit registers
RH registers
R0H to R7H
RL registers
R0L to R7L
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