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FlexBus
20-16
Freescale Semiconductor
Figure 20-7. Basic Read-Bus Cycle
20.4.6.2
Basic Write Bus Cycle
During a write cycle, the device sends data to memory or to a peripheral device.
shows the
write cycle flowchart.
Figure 20-8. Write-Cycle Flowchart
FB_CLK
FB_R/W
S0
S1
S2
S3
FB_ALE
FB_TSIZ[1:0]
TSIZ[1:0]
Mux’d Bus
Non-Mux’d Bus
FB_A[23:0]
FB_D[31:
X
]
FB_AD[31:
X
]
FB_CS
n
, FB_OE,
FB_BE/BWE
n
FB_TA
DATA
DATA
ADDR[23:0]
ADDR[31:
X
]
ADDR[31:
X
]
ADDR[
Y
:0]
S0
FB_AD[
Y
:0]
1. Select the appropriate slave device.
Assert FB_TA (external termination).
3.
1. Negate FB_TA (external termination).
1. Decode address.
1. Set FB_R/W to write.
Assert FB_CS
n
.
2.
1.
(auto acknowledge/internal termination).
Sample FB_TA low.
2.
1. Start next cycle.
ColdFire device
System
Drive data.
3.
2. Place address on FB_AD[31:0].
2. Latch data on FB_AD[31:
X
].
3. Assert FB_ALE.
1. Negate FB_ALE.
FlexBus asserts internal FB_TA
Содержание MCF54455
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Страница 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
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