HD404054 Datasheet, PDF (12/101 Pages) Hitachi Semiconductor – HMCS400-series microcomputers designed to increase program productivity with large-capacity memory

HD404054 Series/HD404094 Series
Functional Description
Registers and Flags
The MCU has nine registers and two flags for CPU operations. They are shown in figure 7 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, no R/W
Program counter
13
Initial value: 0,
no R/W
Stack pointer
Initial value: $3FF, no R/W
(PC)
9
5
1 11 1
3
0
(SPX)
3
0
(SPY)
0
(CA)
0
(ST)
0
0
(SP)
Figure 7 Registers and Flags
Accumulator (A), B Register (B): Four-bit registers used to hold the results from the arithmetic logic unit
(ALU) and transfer data between memory, I/O, and other registers.
W Register (W), X Register (X), Y Register (Y): Two-bit (W) and four-bit (X and Y) registers used for
indirect RAM addressing. The Y register is also used for D-port addressing.
12