M68HC16 Z SERIES
CENTRAL PROCESSING UNIT
USER’S MANUAL
4-35
Figure 4-5 Instruction Execution Model
4.10.1 Microsequencer
The microsequencer controls the order in which instructions are fetched, advanced
through the pipeline, and executed. It increments the program counter and generates
multiplexed external tracking signals IPIPE0 and IPIPE1 from internal signals that con-
trol execution sequence.
4.10.2 Instruction Pipeline
The pipeline is a three stage FIFO that holds instructions while they are decoded and
executed. Depending upon instruction size, as many as three instructions can be in
the pipeline at one time (single-word instructions, one held in stage C, one being exe-
cuted in stage B, and one latched in stage A).
4.10.3 Execution Unit
The execution unit evaluates opcodes, interfaces with the microsequencer to advance
instructions through the pipeline, and performs instruction operations.
A
B
C
MICROSEQUENCER
EXECUTION UNIT
DATA
BUS
INSTRUCTION PIPELINE
IPIPE0
IPIPE1
16 EXEC UNIT MODEL
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