H8SLASH3024F datasheet(61/841 Pages) RENESAS

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Section 2 CPU

Rev. 2.00 Sep 20, 2005 page 23 of 800

REJ09B0260-0200

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.

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