HD404019R Datasheet, PDF (13/65 Pages) Renesas Technology Corp – CMOS 4-bit single-chip microcomputers

Functional Description
HD404019R Series
Registers and Flags
The MCU has nine registers and two flags for the CPU operations (figure 5).
3
0
A
Accumulator
3
0
B
B register
10
W W register
3
0
X
X register
3
0
Y
Y register
3
0
SPX
SPX register
3
0
SPY
SPY register
0
CA Carry flag
0
ST Status flag
13
PC
0
Program counter
9
5
11 1 1
SP
0
Stack pointer
Figure 5 Registers and Flags
Accumulator (A), B Register (B): The 4-bit accumulator and B register hold the results from the
arithmetic logic unit (ALU), and transfer data to/from memory, I/O, and other registers.
W Register (W), X Register (X), Y Register (Y): The 2-bit W register, and the 4-bit X and Y registers
indirectly address RAM. The Y register is also used for D-port addressing.
SPX Register (SPX), SPY Register (SPY): The 4-bit registers SPX and SPY assist the X and Y registers,
respectively.
Carry Flag (CA): The carry flag (CA) stores the overflow from the ALU generated by an arithmetic
operation. It is also affected by the SEC, REC, ROTL, and ROTR instructions.
11