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CHAPTER 2 CPU
2.8 Register Bank
A register bank consists of eight words. The register bank can be used as the following
general-purpose registers for arithmetic operations: byte registers R0 to R7, word
registers RW0 to RW7, and long word registers RL0 to RL3. In addition, the register
bank can be used as instruction pointers.
RL0 to RL3 are used as the linear pointer that directly accesses entire space.
■ Register Bank
Table 2.8-1 lists the functions of the registers. Table 2.8-2 indicates the relationship between the registers.
In the same manner as for an ordinary RAM area, the register bank values are not initialized by a reset. The
status before a reset is maintained. When the power is turned on, however, the register bank will have an
undefined value.
●
Direct page register (DPR) <Initial value: 01
H
>
DPR specifies addr8 to addr15 of the instruction operands in direct addressing mode as shown in Figure
Table 2.8-1 Register Functions
R0 to R7
Used as operands of instructions.
Note: R0 is used as a counter for barrel shift and normalization instructions.
RW0 to RW7
Used as pointers.
Used as operands of instructions.
Note: RW0 is used as a counter for string instructions.
RL0 to RL3
Used as long pointers.
Used as operands of instructions.
Table 2.8-2 Relationship between Registers
RW0
RL0
RW1
RW2
RL1
RW3
R0
RW4
RL2
R1
R2
RW5
R3
R4
RW6
RL3
R5
R6
RW7
R7