Freescale Semiconductor, Inc.
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9
0
1
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CLOCK
1 PRE-
FETCH
2 PRE-
FETCH
3 PRE-
FETCH
3 PRE-
FETCH
BUS
CONTROLLER
WRITE
FOR 1
READ
FOR 2
WRITE
FOR 2
WRITE
FOR 3
INSTRUCTION
CONTROLLER
EA FETCH
ADDQ
ADDQ
TO <EA>
EA CALC
CLR
CLR
<EA>
MOVE A1,(AO)+
EXECUTION
TIME
MOVE.W A1,(AO)+
CLR.W $30(A1)
ADDQ.W #1,(AO)
Figure 5-33. Example 1—Instruction Stream
5.7.2.2 TIMING EXAMPLE 2—BRANCH INSTRUCTIONS. Example 2 shows what
happens when a branch instruction is executed for both the taken and not-taken cases.
(see Figures 5-34 and 5-35). The instruction stream is for a simple limit check with the
variable already in a data register.
Instructions
MOVEQ
CMP.L
BLE.B
#7, D1
D1, D0
NEXT
MOVE.L
D1, (A0)
1
2
3
4
5
4
6
7
8
9
0
1
2
3
CLOCK
1 PRE-
FETCH
2 PRE-
FETCH
PRE-
FETCH
PRE-
FETCH
BUS
CONTROLLER
PRE-
FETCH
WRITE
FOR 3
INSTRUCTION
CONTROLLER
OFFSET
CALC
NEXT
INST.
CMP
MOVEQ
TAKEN
TAKEN
TAKEN
EXECUTION
TIME
MOVEQ
#7,D1
CMP
D1,D0
BLE.B NOT TAKEN
Figure 5-34. Example 2—Branch Taken
MOTOROLA
MC68340 USER’S MANUAL
5- 95
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