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(2) Function
General-purpose registers can be operated in units of eight bits. They can also be operated in units of 16 bits,
that is, a pair of eight-bit registers can be operated as a single unit (AX, BC, DE, HL).
Each register can temporarily hold operation results or can be used as an operand of an arithmetic/logical
instruction between registers.
General-purpose registers are grouped into four register banks. By separating the register banks to be used
for ordinary operation from those for interrupt handling, an efficient program can be created.
The registers have different functions as described below:
A (R1)
: Central register for the transfer of 8-bit data or arithmetic/logical operations. This
AX (RP0)
: Central register for the transfer of 16-bit data or arithmetic/logical operations
X (R0)
: Register that can hold bit data
B (R3)
: Register with the functions of a loop counter. The register can be used by the DBNZ
C (R2)
: Register with the functions of a loop counter. The register can be used by the DBNZ
DE (RP2), HL (RP3) : Registers with the functions of a pointer. The registers specify a base address for register
Each register can be identified by a name representing its function (X, A, C, B, E, D, L, H, AX, BC, DE, HL) or
by an absolute name (R0 to R7, RP0 to RP3). For details of the relationship between the function names and
absolute names, see Table 3-3.
Function name
register can also hold bit data.
The register can also hold the offset value for indexed addressing.
instruction.
This register can also hold the offset value for indexed addressing.
instruction.
indirect addressing and base addressing.
This register can also hold the offset value for indexed addressing.
Table 3-3 Function Names and Absolute Names
Absolute name
X
R0
A
R1
C
R2
R3
B
E
R4
D
R5
L
R6
R7
H
Chapter 3 CPU Function
Function name
Absolute name
AX
RP0
BC
RP1
DE
RP2
RP3
HL
3
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