E202075_HD404889 Datasheet, PDF (38/202 Pages) Renesas Technology Corp – Low-Voltage AS Microcomputers with On-Chip LCD Circuit

HD404889/HD404899/HD404878/HD404868 Series
Functional Description
Registers and Flags
The MCU has nine registers and two flags for CPU operations. they are shown in figure 8 and described
below.
Accumulator
Initial value: Undefined, R/W
B register
Initial value: Undefined, R/W
W register
Initial value: Undefined, R/W
X register
Initial value: Undefined, R/W
Y register
Initial value: Undefined, R/W
SPX register
Initial value: Undefined, R/W
SPY register
Initial value: Undefined, R/W
Carry flag
Initial value: Undefined, R/W
Status flag
Program counter
Initial value: $0000,
no R/W
Stack pointer
Initial value: $3FF, no R/W
Initial value: 1, no R/W
13
(PC)
9
5
1111
3
0
(A)
3
0
(B)
1
0
(W)
3
0
(X)
3
0
(Y)
3
0
(SPX)
3
0
(SPY)
0
(CA)
0
(ST)
0
0
(SP)
Figure 8 Registers and Flags
Accumulator (A) and B register (B):
The accumulator and B register are 4-bit registers used to hold the result of an ALU operation, and for data
transfer to or from memory, an I/O area, or another register.
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