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FlexBus
Freescale Semiconductor
20-13
The table below lists the supported combinations of address and data bus widths.
20.4.5
Bus Cycle Execution
, basic bus operations occur in four clocks:
1. S0: At the first clock edge, the address, attributes, and FB_ALE are driven.
2. S1: FB_CS
n
is asserted at the second rising clock edge to indicate the device selected; by that time,
the address and attributes are valid and stable. FB_ALE is negated at this edge.
For a write transfer, data is driven on the bus at this clock edge and continues to be driven until one
clock cycle after FB_CS
n
negates. For a read transfer, data is also driven into the device during this
cycle.
External slave asserts FB_TA at this clock edge.
3. S2: Read data and FB_TA are sampled on the third clock edge. FB_TA can be negated after this
edge and read data can then be tri-stated.
4. S3: FB_CS
n
is negated at the fourth rising clock edge. This last clock of the bus cycle uses what
would be an idle clock between cycles to provide hold time for address, attributes, and write data.
Table 20-8. FlexBus Multiplexed Operating Modes
Port Size and Phase
FB_AD
[31:24]
[23:16]
[15:8]
[7:0]
32
-bit
Address phase
Address
Data phase
Data
16
-bit
Address phase
Address
Data phase
Data
Address
8-bit
Address phase
Address
Data phase
Data
Address
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...