Datasheet

Section 2 CPU
Rev. 3.00 Mar. 15, 2006 Page 12 of 526
REJ09B0060-0300
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 the stack pointer and the stack area.