HD404669 Datasheet, PDF (18/142 Pages) Hitachi Semiconductor – Low-Voltage AS Microcomputers with On-Chip DTMF Generation Circuit

HD404669 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
3
0
(A)
B register
W register
X register
Y register
Initial value: Undefined, R/W
Initial value: Undefined, R/W
Initial value: Undefined, R/W
Initial value: Undefined, R/W
3
0
(B)
10
(W)
3
0
(X)
3
0
(Y)
SPX register
Initial value: Undefined, R/W
SPY register
Initial value: Undefined, R/W
Carry
Initial value: Undefined, R/W
Status
Initial value: 1, R/W not possible
Program counter
13
Initial value: $0000,
R/W not possible
Stack pointer
Initial value: $3FF, R/W not possible
(PC)
9
5
1 11 1
3
0
(SPX)
3
0
(SPY)
0
(CA)
0
(ST)
0
0
(SP)
Figure 8 Registers and Flags
Accumulator (A) and B Register (B): A and B are 4-bit registers, and are used to hold the results of ALU
(arithmetic and logical unit) operations and to transfer data between memory, I/O ports, and other registers.
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