
CPU16
REFERENCE MANUAL
INSTRUCTION SET
MOTOROLA
5-23
To make certain that conditions for termination of LPSTOP and WAI are correct, inter-
rupts are not recognized until after the instruction following ANDP, ORP, TAP, and
TDP executes. This prevents interrupt exception processing during the period after the
mask changes but before the following instruction executes.
5.12 Background Mode and Null Operations
Background debug mode is a special CPU16 operating mode that is used for system
development and debugging. Executing BGND when BDM is enabled puts the CPU16
in this mode. For complete information refer to
SECTION 10 DEVELOPMENT SUP-
PORT
.
Null operations are often used to replace other instructions during software debugging.
Replacing conditional branch instructions with BRN, for instance, permits testing a de-
cision-making routine without actually taking the branches.
5.13 Comparison of CPU16 and M68HC11 Instruction Sets
Most M68HC11 instructions are a source-code compatible subset of the CPU16
instruction set. However, certain M68HC11 instructions have been replaced by func-
tionally equivalent CPU16 instructions, and some M68HC11 instructions operate dif-
ferently in the CPU16.
APPENDIX A COMPARISON OF CPU16/M68HC11 CPU
ASSEMBLY LANGUAGE
gives detailed information.
Table 5-33
shows M68HC11 instructions that have either been replaced by CPU16 in-
structions or that operate differently in the CPU16. Replacement instructions are not
identical to M68HC11 instructions; M68HC11 code must be altered to establish proper
preconditions.
All CPU16 instruction cycle counts and execution times differ from those of the
M68HC11.
SECTION 6 INSTRUCTION GLOSSARY
gives information on instruction
cycles. See
SECTION 8 INSTRUCTION TIMING
for information regarding calculation
of instruction cycle times.
Table 5-31 Stop and Wait Summary
Mnemonic
Function
Operation
LPSTOP
Low Power Stop
If S
then STOP
else NOP
WAI
Wait for Interrupt
WAIT
Table 5-32 Background Mode and Null Operations
Mnemonic
BGND
Function
Operation
If BDM enabled
enter BDM;
else, illegal instruction
If 1 = 0, branch
If 1 = 0, branch
—
Enter Background Debugging Mode
BRN
LBRN
NOP
Branch Never
Long Branch Never
Null operation
F
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n
.