Renesas Hitachi H8S/2191, Hardware Manual

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Rev. 2.0, 11/00, page 25 of 1037
2.4.2 General Registers
The CPU has eight 32-bit general registers. These general registers are all functionally alike 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. 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 general 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.
Figure 2.8 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 2.8 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 2.9 shows the
stack.