Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 480 of 547
NXP Semiconductors
UM10398
Chapter 28: LPC111x/LPC11Cxx Appendix: ARM Cortex-M0 reference
28.5.3.6 Conditional execution
Most data processing instructions update the condition flags in the Application Program
Status Register (APSR) according to the result of the operation, see Section
. Some
instructions update all flags, and some only update a subset. If a flag is not updated, the
original value is preserved. See the instruction descriptions for the flags they affect.
You can execute a conditional branch instruction, based on the condition flags set in
another instruction, either:
• immediately after the instruction that updated the flags
• after any number of intervening instructions that have not updated the flags.
On the Cortex-M0 processor, conditional execution is available by using conditional
branches.
This section describes:
• Section 28.5.3.6.1 “The condition flags”
• Section 28.5.3.6.2 “Condition code suffixes”.
28.5.3.6.1 The condition flags
The APSR contains the following condition flags:
N — Set to 1 when the result of the operation was negative, cleared to 0 otherwise.
Z — Set to 1 when the result of the operation was zero, cleared to 0 otherwise.
C — Set to 1 when the operation resulted in a carry, cleared to 0 otherwise.
V — Set to 1 when the operation caused overflow, cleared to 0 otherwise.
For more information about the APSR see Section 28–28.4.1.3.5
.
A carry occurs:
• if the result of an addition is greater than or equal to 2
32
• if the result of a subtraction is positive or zero
• as the result of a shift or rotate instruction.
Overflow occurs when the sign of the result, in bit[31], does not match the sign of the
result had the operation been performed at infinite precision, for example:
• if adding two negative values results in a positive value
• if adding two positive values results in a negative value
• if subtracting a positive value from a negative value generates a positive value
• if subtracting a negative value from a positive value generates a negative value.
The Compare operations are identical to subtracting, for CMP, or adding, for CMN, except
that the result is discarded. See the instruction descriptions for more information.
28.5.3.6.2 Condition code suffixes
Conditional branch is shown in syntax descriptions as B{cond}. A branch instruction with a
condition code is only taken if the condition code flags in the APSR meet the specified
condition, otherwise the branch instruction is ignored. shows the condition codes to use.