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Rev. 1.0, 07/01, page 11 of 372
2.2.1 General Registers
The H8/300H CPU has eight 32-bit general registers. These general registers are all functionally
identical and can be used as both address registers and data 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. Figure 2-3 illustrates
the usage of the general registers. When the general registers are used as 32-bit registers or 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 of sixteen 16-bit
registers. The E registers (E0 to E7) are also referred to as extended registers.
The R registers divide into 8-bit registers designated by the letters RH (R0H to R7H) and RL (R0L
to R7L). These registers are functionally equivalent, providing a maximum of sixteen 8-bit
registers.
The usage of each register can be selected independently.
• Address registers
• 32-bit registers
• 16-bit registers • 8-bit registers
ER registers
(ER0 to ER7)
E registers (extended registers)
(E0 to E7)
R registers
(R0 to R7)
RH registers
(R0H to R7H)
RL registers
(R0L to R7L)
Figure 2-3 Usage of General Registers
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 2-4 shows the
relationship between stack pointer and the stack area.