NEC PD78214 - Manual (Page 78)

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Chapter 3 CPU Function
3
(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
register can also hold bit data.
The register can also hold the offset value for indexed addressing.
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
instruction.
This register can also hold the offset value for indexed addressing.
C (R2) : Register with the functions of a loop counter. The register can be used by the DBNZ
instruction.
DE (RP2), HL (RP3) : Registers with the functions of a pointer. The registers specify a base address for register
indirect addressing and base addressing.
This register can also hold the offset value for indexed addressing.
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.
Table 3-3 Function Names and Absolute Names
X
A
C
B
E
D
L
H
Function name Absolute name
R0
R1
R2
R3
R4
R5
R6
R7
AX
BC
DE
HL
Function name Absolute name
RP0
RP1
RP2
RP3