MOTOROLA
INSTRUCTION GLOSSARY
CPU12
6-46
REFERENCE MANUAL
Operation:
(PC)
+
$0002
⇒
PC
Description:
Never branches. BRN is effectively a 2-byte NOP that requires one cycle
to execute. BRN is included in the instruction set to provide a comple-
ment to the BRA instruction. The instruction is useful during program de-
bug, to negate the effect of another branch instruction without disturbing
the offset byte. A complement for BRA is also useful in compiler imple-
mentations.
Execution time is longer when a conditional branch is taken than when
it is not, because the instruction queue must be refilled before execution
resumes at the new address. Since the BRN branch condition is never
satisfied, the branch is never taken, and only a single program fetch is
needed to update the instruction queue.
See
for details of branch execution.
Condition Codes and Boolean Formulas:
None affected.
Addressing Modes, Machine Code, and Execution Times:
BRN
Branch Never
BRN
S
X
H
I
N
Z
V
C
–
–
–
–
–
–
–
–
Source Form
Address Mode
Object Code
Cycles
Access Detail
BRN
rel8
REL
21 rr
1
P
Summary of Contents for CPU12
Page 8: ...MOTOROLA CPU12 viii REFERENCE MANUAL ...
Page 14: ...MOTOROLA INTRODUCTION CPU12 1 4 REFERENCE MANUAL ...
Page 20: ...MOTOROLA OVERVIEW CPU12 2 6 REFERENCE MANUAL ...
Page 38: ...MOTOROLA INSTRUCTION QUEUE CPU12 4 6 REFERENCE MANUAL ...
Page 300: ...MOTOROLA DEVELOPMENT AND DEBUG SUPPORT CPU12 8 16 REFERENCE MANUAL ...
Page 338: ...MOTOROLA MEMORY EXPANSION CPU12 10 8 REFERENCE MANUAL ...
Page 364: ...MOTOROLA INSTRUCTION REFERENCE CPU12 A 26 REFERENCE MANUAL ...
Page 386: ...MOTOROLA HIGH LEVEL LANGUAGE SUPPORT CPU12 C 6 REFERENCE MANUAL ...
Page 438: ...MOTOROLA SUMMARY OF CHANGES CPU12 S 2 REFERENCE MANUAL ...
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