UPD17010 datasheet(49/424 Pages) NEC

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µPD17010

5.8.2 Function of program status word

The program status word is a register that sets the condition for the operation of the ALU (Arithmetic Logic Unit)

or transfer instruction or indicates the result of an operation.

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

For details of the operation, refer to 7. ALU (ARITHMETIC LOGIC UNIT) BLOCK.

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

RPL

PSW

(RP)

Program Status

Word (PSWORD)

Flag Name

Index enable flag

(IXE)

Modifies address of data memory when data memory

manipulation instruction is executed

0: Does not modify

1: Modifies

Zero flag

(Z)

Indicates that resultof arithmeticoperation is zero.

Note that status of 0 and 1 of this flag differs depending on

contents of compare flag.

Carry flag

(CY)

Indicates occurrence of carry or borrow as result of exe-

cuting addition or subtraction instruction.

Reset to 0 if carry or borrow does not occur.

Set to 1 if carry or borrow occurs.

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

Compare flag

(CMP)

Function

This flag specifies whether or not resultof arithmetic

operation isstored to data memory or general regizster.

0: Stores result

1: Does not store result

BCD flag

(BCD)

This flag specifies whether arithmetic operation is performed

in binary or decimal

1: Binary operation

0: Decimal operation

5.8.3 Notes on using program status word

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

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

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

is stored to PSW.

5.9 Notes on Using System Register

Data of the system register that is fixed to “0” is not affected in any way even if a write instruction is executed to

it.

If this data is read, “0” is always read.

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