PM0056 datasheet(58/156 Pages) STMICROELECTRONICS

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The Cortex-M3 instruction set

PM0056

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DocID15491 Rev 5

Most instructions update the status flags only if the S suffix is specified. See the instruction

descriptions for more information.

Condition code suffixes

The instructions that can be conditional have an optional condition code, shown in syntax

descriptions as {cond}. Conditional execution requires a preceding IT instruction. An

instruction with a condition code is only executed if the condition code flags in the APSR

meet the specified condition. Table 23 shows the condition codes to use.

You can use conditional execution with the IT instruction to reduce the number of branch

instructions in code.

Table 23 also shows the relationship between condition code suffixes and the N, Z, C, and V

flags.

Specific example 1: Absolute value shows the use of a conditional instruction to find the

absolute value of a number. R0 = ABS(R1).

Specific example 1: Absolute value

MOVSR0, R1; R0 = R1, setting flags

IT MI; IT instruction for the negative condition

RSBMIR0, R1, #0; If negative, R0 = -R1

Table 23. Condition code suffixes

Suffix

Flags

Meaning

Z = 1

Equal

Z = 0

Not equal

CS or HS

C = 1

Higher or same, unsigned

≥

CC or LO

C = 0

Lower, unsigned <

N = 1

Negative

N = 0

Positive or zero

V = 1

Overflow

V = 0

No overflow

C = 1 and Z = 0

Higher, unsigned >

C = 0 or Z = 1

Lower or same, unsigned

≤

N = V

Greater than or equal, signed

≥

!= V

Less than, signed <

Z = 0 and N = V

Greater than, signed >

Z = 1 and N

!= V

Less than or equal, signed

≤

Can have any value

Always. This is the default when no suffix is specified.

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