Datasheet

78K0/Ix2 CHAPTER 3 CPU ARCHITECTURE
R01UH0010EJ0500 Rev.5.00 56
Feb 28, 2012
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.
Figure 3-12. Configuration of General-Purpose Registers
(a) Function name
Register bank 0
Register bank 1
Register bank 2
Register bank 3
FEFFH
FEF8H
FEE0H
HL
DE
BC
AX
H
15 0 7 0
L
D
E
B
C
A
X
16-bit processing 8-bit processing
FEF0H
FEE8H
(b) Absolute name
Register bank 0
Register bank 1
Register bank 2
Register bank 3
FEFFH
FEF8H
FEE0H
RP3
RP2
RP1
RP0
R7
15 0 7 0
R6
R5
R4
R3
R2
R1
R0
16-bit processing 8-bit processing
FEF0H
FEE8H