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CHAPTER 3 CPU
3.3 General-purpose Registers
The general-purpose registers are a memory block made up of banks, with 8 x 8-bit
registers per bank.
The register bank pointer (RP) is used to specify the register bank.
The function permits the use of up to 32 banks, but the number of banks that can
actually be used depends on how much RAM the device has.
Register banks are valid for interrupt processing, vector call processing, and
subroutine calls.
■ Structure of general-purpose registers
• The general-purpose registers are 8 bits and located in the register banks of the general-purpose register
area (in RAM).
• One bank contains eight registers (R0 to R7) and up to a total of 32 banks. However, the number of
banks available for general-purpose registers is limited on some products if internal RAM only is used.
• The register bank currently in use is specified by the register bank pointer (RP). The lower three bits of
the operation code specify general-purpose register 0 (R0) to general-purpose register 7 (R7).
Figure 3.3-1 "Register bank structure" shows the register bank structure.
Figure 3.3-1 Register bank structure
See Section 3.1.1 "Special Areas" for the general-purpose register area available for each product.
Lower 3 bits of
the operation code
*: The top address of a register bank = 0100
H + 8 x (upper 5 bits of RP)
R0
R1
R2
R3
R4
R5
R6
R7
R0
R7
R0
R7
:
:
:
:
:
000
001
010
011
100
101
110
111
000
111
000
111
100
H*
108
H*
1FFH
1F8H*
:
:
:
:
:
Bank 0
(RP="00000---
B")
Bank 1
(RP="00001---
B")
Bank 31
(RP="11111---
B"
)
Bank 2
to
Bank 30
32 banks
(RAM area)
The number of banks is limited
on available RAM size.