FlexBus
20-14
Freescale Semiconductor
20.4.5.1
Data Transfer Cycle States
An on-chip state machine controls the data-transfer operation in the device.
state-transition diagram for basic read and write cycles.
Figure 20-5. Data-Transfer-State-Transition Diagram
describes the states as they appear in subsequent timing diagrams.
20.4.6
FlexBus Timing Examples
NOTE
Because this device shares the FlexBus signals with the PCI controller, all
signals, except the chip selects, tristate between bus cycles.
Table 20-10. Bus Cycle States
State
Cycle
Description
S0
All
The read or write cycle is initiated. On the rising clock edge, the device places a valid address on
FB_AD[
:0], asserts FB_ALE, and drives FB_R/W high for a read and low for a write.
S1
All
FB_ALE is negated on the rising edge of FB_CLK, and FB_CS
n
is asserted. Data is driven on
FB_AD[31:
X
] for writes, and FB_AD[31:
X
] is tristated for reads. Address continues to be driven
on the FB_AD pins that are unused for data.
If FB_TA is recognized asserted, then the cycle moves on to S2. If FB_TA is not asserted
internally or externally, then the S1 state continues to repeat.
Read
Data is driven by the external device before the next rising edge of FB_CLK (the rising edge that
begins S2) with FB_TA asserted.
S2
All
For internal termination, FB_CS
n
is negated and the internal system bus transfer is completed.
For external termination, the external device should negate FB_TA, and the FB_CS
n
chip select
negates after the rising edge of FB_CLK at the end of S2.
Read
The processor latches data on the rising clock edge entering S2. The external device can stop
driving data after this edge. However, data can be driven until the end of S3 or any additional
address hold cycles.
S3
All
Address, data, and FB_R/W go invalid off the rising edge of FB_CLK at the beginning of S3,
terminating the read or write cycle.
S0
S1
S2
Wait States
S3
Next Cycle
31
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 ...