Hitachi H8/3008, Hardware Manual

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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
• 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 2.4 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 2.5 shows the
stack.