UPD17072 datasheet(39/228 Pages) RENESAS

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µPD17072,17073

5.4.2 Functions of program status word

The program status word sets conditions, under which the ALU (Arithmetic Logic Unit) performs arithmetic or

transfer operations, and indicates the results of the operations.

Table 5-2 outlines the function of each flag of the program status word.

For details, refer to 7. ALU (Arithmetic Logic Unit) BLOCK.

Table 5-2. Functional Outline of Each Flag of Program Status Word

Flag name

Function

Zero flag (Z)

Carry flag (CY)

Compare flag (CMP)

BCD flag (BCD)

5.4.3 Notes on using program status word

When an arithmetic operation (addition or subtraction) instruction is executed to the program status word, the result

of the arithmetic operation is stored in the program status word.

Even if an operation that generates a carry has been executed, for example, if the result of the operation is 0000B,

0000B is stored in PSW.

5.5 Notes on Using System Register

The data in the system register which are fixed to “0” are not influenced even when a write instruction is executed.

When these data are read, “0” is always read.

Indicates that the result of arithmetic operation is 0. Con-

dition under which this flag is set differs depending on

contents of compare flag.

Indicates occurrence of carry or borrow as a result of

executing addition or subtraction instruction.

Reset (0) when carry or borrow does not occur. Set (1) when

carry or borrow occurs. Also used as shift bit of "RORC r"

instruction.

Stores or does not store result of arithmetic operation in

data memory or general register.

0: Stores result

1: Does not store result

Executes arithmetic operation in decimal.

0: Executes binary operation

1: Executes decimal operation

(RP)

Program status

word (PSWORD)

RPL

PSW

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