AN2662 Freescale Semiconductor / Motorola, AN2662 Datasheet - Page 25

• Manufacturer Part Number: AN2662
• Description: Migrating from PowerQUICC II to PowerQUICC III
• Manufacturer: Freescale Semiconductor / Motorola

New Features on PowerQUICC III
New Features on PowerQUICC III
The main difference between the PCI block implemented on the PowerQUICC II to that of the
PowerQUICC III is that the PowerQUICC II implements a 32-bit addressable PCI interface and can only
support three Request/Grant signal pairs i.e. only a maximum of three external PCI masters can be
supported. Apart from these additional address and Request/Grant signals, all other PCI signals
implemented on the PowerQUICC II remain the same on PowerQUICC III.
4.7.1 PCI & PCI-X System Differences
Perhaps the most obvious difference between PCI and PCI-X is the speed increase of the interface which
can now run up to 133MHz. PCI-X is a latch-to-latch based protocol which allows more timing margin for
propagation delay and receiver logic. This is shown below in Figure 12.
Unlike the PCI specification, PCI-X is a split transaction based protocol which has separate arbitration
transactions for both bus request and response. Again, this helps to improve bus latency and utilization.
Since the maximum transaction size in a PCI-X system is limited to 4K bytes, the worst case system latency
dramatically improves. Also, bus utilization is improved by the restriction of both targets and initiators in
inserting wait states. Targets cannot insert wait states after the first data beat and both initiators and targets
can only end a burst on a naturally aligned 128-byte boundary. Each transaction in a PCI-X system carries
a byte count and the identity of the initiator that was not possible in the PCI specification. Hence, PCI-X
systems offer better buffer management capabilities and make more efficient use of the available system
memory.
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PCI-X
PCI
Transmitter
Transmitter
Asserts
Asserts
Signal
Signal
Width
32-bit
64-bit
64-bit
64-bit
PCI
Migrating from PowerQUICC II to PowerQUICC III
Delay
Freescale Semiconductor, Inc.
Prop
For More Information On This Product,
Figure 13. PCI/PCI-X System Comparison
Delay
Prop
Figure 12. PCI/PCI-X Timing Analysis
Receiver
Frequency
Logic
100 MHz
133 MHz
33 MHz
66 MHz
PCI
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Receiver
Responds
Samples
Receiver
Bandwidth
1066 MB/s
133 MB/s
528 MB/s
800 MB/s
PCI
Receiver
Logic
Slots
PCI
N/A
N/A
Responds
Receiver
PCI-X
Slots
N/A
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