General-Purpose Registers - NEC 78K0 Series User Manual

3.2.2 General-purpose registers

General-purpose registers are mapped at particular addresses (FEE0H to FEFFH) of the data memory. The
general-purpose registers consists of 4 banks, each bank consisting of eight 8-bit registers (X, A, C, B, E, D, L, and H).
Each register can be used as an 8-bit register, and two 8-bit registers can also be used in a pair as a 16-bit register
(AX, BC, DE, and HL).
These registers can be described in terms of function 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 by 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 interrupts for each bank.
FEFFH
Register bank 0
FEF8H
Register bank 1
FEF0H
Register bank 2
FEE8H
Register bank 3
FEE0H
FEFFH
Register bank 0
FEF8H
Register bank 1
FEF0H
Register bank 2
FEE8H
Register bank 3
FEE0H
CHAPTER 3 CPU ARCHITECTURE
Figure 3-21. Configuration of General-Purpose Registers
(a) Function name
16-bit processing
15
(b) Absolute name
15
Preliminary User's Manual U17260EJ3V1UD
HL
DE
BC
AX
0
16-bit processing
RP3
RP2
RP1
RP0
0
8-bit processing
H
L
D
E
B
C
A
X
7 0
8-bit processing
R7
R6
R5
R4
R3
R2
R1
R0
7 0
71