General-Purpose Registers - NEC 78K/0 Series User Manual

2.2 General-Purpose Registers

General-purpose registers are mapped at particular addresses (FEE0H to FEFFH) of the data memory. These
registers consist of 4 banks, each bank consisting of eight 8-bit registers (X, A, C, B, E, D, L and H).
In addition that each register can be used as an 8-bit register, two 8-bit registers in pairs can be used as a 16-
bit register (AX, BC, DE and HL).
General-purpose registers can be described in terms of functional names (X, A, C, B, E, D, L, H, AX, BC, DE
and HL) and absolute names (R0 to R7 and RP0 to RP3).
Register banks to be used for instruction execution are set with the CPU control instruction (SEL RBn). Because
of the 4-register bank configuration, an efficient program can be created by switching between a register for normal
processing and a register for processing upon interrupt generation for each bank.
Table 2-1. General-Purpose Register Absolute Address Correspondence Table
Bank Name Register
Functional
Name
BANK0 H
L
D
E
B
C
A
X
BANK1 H
L
D
E
B
C
A
X
CHAPTER 2 REGISTERS
Absolute Address
Absolute
Name
R7 FEFFH
R6 FEFEH
R5 FEFDH
R4 FEFCH
R3 FEFBH
R2 FEFAH
R1 FEF9H
R0 FEF8H
R7 FEF7H
R6 FEF6H
R5 FEF5H
R4 FEF4H
R3 FEF3H
R2 FEF2H
R1 FEF1H
R0 FEF0H
User's Manual U12326EJ4V0UM
Bank Name Register
Functional
Name
BANK2 H
L
D
E
B
C
A
X
BANK3 H
L
D
E
B
C
A
X
Absolute Address
Absolute
Name
R7 FEEFH
R6 FEEEH
R5 FEEDH
R4 FEECH
R3 FEEBH
R2 FEEAH
R1 FEE9H
R0 FEE8H
R7 FEE7H
R6 FEE6H
R5 FEE5H
R4 FEE4H
R3 FEE3H
R2 FEE2H
R1 FEE1H
R0 FEE0H
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