General-Purpose Registers - Fujitsu Semiconductor Controller MB89950/950A Hardware Manual

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.
I 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.
*: The top address of a register bank = 0100
See Section 3.1.1 "Special Areas" for the general-purpose register area available for each product.
Figure 3.3-1 Register bank structure
Lower 3 bits of
the operation code
R0 000
100 *
H
R1 001
R2 010
R3 011
R4 100
R5 101
R6 110
R7 111
108 *
R0 000
H
: :
R7 111
: :
: :
: :
1F8 *
R0 000
H
: :
R7 111
1FF
H
+ 8 x (upper 5 bits of RP)
H
Bank 0
(RP="00000--- ")
B
32 banks
(RAM area)
The number of banks is limited
on available RAM size.
Bank 1
(RP="00001--- ")
B
Bank 2
to
Bank 30
Bank 31
(RP="11111--- ")
B
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