Mini-FlexBus
Freescale Semiconductor
11-12
MCF51CN128 Reference Manual, Rev. 6
Figure 11-7. Basic Read-Bus Cycle
11.4.6.2
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 11-8. Write-Cycle Flowchart
FB_CLK
FB_R/W
S0
S1
S2
S3
FB_ALE
Mux’d Bus
Non-Mux’d Bus
FB_A[19:0]
FB_D[7:0]
FB_AD[
X
:0]
FB_CS
n
, FB_OE
DATA
DATA
ADDR[19:0]
ADDR[
X
:0]
ADDR[19:
X+1
]
S0
FB_AD[19:
X+1
]
1. Select the appropriate slave device.
1. Decode address.
1. Set FB_R/W to write.
Assert FB_CS
n
.
2.
1.
1. Start next cycle.
ColdFire device
System
Drive data.
3.
2. Place address on FB_AD[19:0].
2. Latch data on FB_AD[
X
:0].
3. Assert FB_ALE.
1. Negate FB_ALE.
Mini-FlexBus asserts internal transfer
acknowledge (auto-acknowledge).
