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L-Bus Show Cycle Support
11.7.3
Show Cycle Protocol
The L2U module behaves as both a master and a slave on the U-bus during show cycles.
The L2U starts the U-bus transfer as a bus master and then completes the address phase and
data phase of the cycle as a slave. The L2U follows U-bus protocol of in-order termination
of the data phase.
The USIU can control the start of show cycles on the U-bus by asserting the no-show cycle
indicator. This will cause the L2U module to release the U-bus for at least one clock before
retrying the show cycle.
11.7.4
L-Bus Write Show Cycle Flow
The L2U performs the following sequence of actions for an L-bus-write show cycle.
1. Arbitrates for the L-bus to prevent any other L-bus cycles from starting
2. Latches the address and the data of the L-bus access, along with all address
attributes
3. Waits for the termination of the L-bus access and latches the termination status
(data error)
4. Arbitrate for the U-bus, and when granted, starts the U-bus access, asserting show
cycle request on the U-bus, along with address, attributes and the write data. The
L2U module provides address recognition and acknowledgment for the address
phase. If the no-show cycle indicator from the U-bus is asserted, the L2U does not
start the show cycle. The L2U module releases the U-bus until the no-show cycle
indicator is negated and then arbitrates for the U-bus again.
5. When the L2U module has U-bus data bus grant, it drives the data phase
termination handshakes on the U-bus.
6. Releases the L-bus
11.7.5
L-Bus Read Show Cycle Flow
The L2U performs the following sequence of actions for an L-bus read show cycle.
1. Arbitrates for the L-bus to prevent any other L-bus cycle from starting
2. Latches the address of the L-bus access, along with all address attributes
3. Waits for the data phase termination on the L-bus and latches the read data, and the
termination status from the L-bus
4. Arbitrates for the U-bus, and when granted, starts the U-bus access, asserting the
show cycle request on the U-bus, along with address attributes. The L2U module
provides address recognition/acknowledgment for the address phase. If the
no-show cycle indicator from the U-bus is asserted, the L2U does not start the show
cycle. The L2U module releases the U-bus until the no-show cycle indicator is
negated and then arbitrates for the U-bus again.
11-12
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
MPC533 Reference Manual
MOTOROLA
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