PM0044 datasheet(121/162 Pages) STMICROELECTRONICS

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PM0044

STM8 instruction set

Doc ID 13590 Rev 3

121/162

Syntax

NEG dst

e.g. NEG (X)

Operation

dst <= (dst XOR FF) + 1, or 00 - dst

Description

The destination byte is read, then each bit is toggled (inverted), and the

result is incremented before it is written at the destination byte. The

destination is either a memory byte or a register. The Carry is cleared if the

result is zero. This instruction is used to negate signed values. This

instruction is compact, and does not affect any register when used with

RAM variables.

Instruction overview

⇒

R7.R6.R5.R4.R3.R2.R1.R0

Set if there is an arithmetic overflow on the 8-bit representation of the

result. The V bit will set when the content of "dst" was $80 (-128) prior to

the NEG operation, cleared otherwise.

⇒

Set if bit 7 of the result is set (negative value), cleared otherwise.

⇒

R7.R6.R5.R4.R3.R2.R1.R0

Set if the result is zero (0x00), cleared otherwise.

⇒

R7+R6+R5+R4+R3+R2+R1+R0

Set if a borrow in the implied subtraction from zero, cleared otherwise. The

C bit will be set in all cases except when the contents of "dst" was $00 prior

to the NEG operation.

Detailed description

NEG

Negate (Logical 2’s complement)

NEG

mnem

dst

Affected condition flags

VI1

NEG

Mem

NEG

dst

Asm

lgth

Op-code(s)

ST7

ANEG A

✗

shortmem

NEG $F5

✗

longmem

NEG $F5C2

(X)

NEG(X)

✗

(shortoff,X)

NEG($F5,X)

✗

(longoff,X)

NEG($F5C2,X)

(Y)

NEG(Y)

✗

(shortoff,Y)

NEG($F5,Y)

✗

(longoff,Y)

NEG($F5C2,Y)

(shortoff,SP)

NEG($F5,SP)

[shortptr.w]

NEG($F5)

✗

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