7480 datasheet(36/337 Pages) RENESAS

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7480 Group and 7481 Group User's Manual

1-19

HARDWARE

(5)

Break Flag B (bit 4)

This flag recognizes whether an interrupt occurs by using the BRK instruction. The contents of

processor status register are pushed onto the stack when the following occurs;

• the contents of this flag is set to ‘1’ when an interrupt occurs by using the BRK instruction, or

• this flag is set to ‘0’ by the all other interrupts.

There is no instruction that can affect the content of this flag.

(6)

Index X Mode Flag T (bit 5)

When this flag is ‘0’, operation is performed between the accumulator and memories. When this flag

is ‘1’, operation is directly done between memories without using the accumulator. This flag is set

to ‘1’ by using the SET instruction and cleared to ‘0’ by using the CLT instruction.

Note: This flag is undefined at reset; it is therefore necessary to initialize this flag because it directly

affects the result of operation.

(7)

Overflow Flag V (bit 6)

This flag is used in adding or subtracting an 8-bit word as signed binary digits. When the result of

addition or subtraction exceeds the range of +127 to -128, this flag is set to ‘1’. When the BIT

instruction is executed, the content of bit 6 of the activated memory is written to the flag.

This flag is cleared to ‘0’ by using the CLV instruction. However, there is no instruction that can set

this flag to ‘1’.

In the decimal mode, this flag is invalid.

(8)

Negative Flag N (bit 7)

When the result of arithmetic, logical or transfer operation is negative (bit 7 is ‘1’), this flag is set to

‘1’. When the BIT instruction is executed, the content of bit 7 of the activated memory is written to

the flag.

There is no instruction that can directly affect the content of this flag.

In the decimal mode, this flag is invalid.

Table 1.7.2 Instructions to Set Flags of Processor Status Register to ‘1’ or ‘0’

1.7 Central Processing Unit (CPU)

Instructions to Set

Flags to ‘1’

Instructions to Set

Flags to ‘0’

C Flag

SEC

CLC

Z Flag

–

I Flag

SEI

CLI

D Flag

SED

CLD

B Flag

–

T Flag

SET

CLT

V Flag

–

CLV

N Flag

–

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