UPD17708 datasheet(55/356 Pages) NEC

55 / 356 page

µPD17704, 17705, 17707, 17708, 17709

5.8.2 Function of program status word

The program status word is a register that sets the conditions under which the ALU (Arithmetic Logic Unit)

executes an operation or data transfer, or indicates the result of an operation.

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. Outline of Function of Each Flag of Program Status Word

5.8.3 Cautions on using program status word

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

of the arithmetic operation is stored.

For example, even if an operation that generates a carry is executed, if the result of the operation is 0000B,

0000B is stored to the PSW.

Program Status

Word (PSWORD)

RPL

PSW

Flag Name

Index enable flag

(IXE)

Zero flag

(Z)

Carry flag

(CY)

Compare flag

(CMP)

BCD flag

(BCD)

Function

Modifies address of data memory when data memory

manipulation instruction is exeuted.

0 : Does not modify

1 : Modifies

Indicates result of arithmetic operation is zero.

Status of this flag differs depending on contents of compare

flag.

Indicates occurrence of carry or borrow as result of execution

of addition or subtraction instruction.

This flag is reset to 0 if no carry or borrow occurs.

It is set to 1 if carry or borrow occurs.

This flag is also used as shift bit of “RORC r” instruction.

Indicates whether result of arithmetic operation is stored to

data memory or general register.

0 : Stores result.

1 : Does not store result.

Indicates whether arithmetic operation is performed in decimal

or binary.

0 : Binary operation

1 : Decimla operation

(RP)

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