11-12
MPC561/MPC563 Reference Manual
MOTOROLA
L-Bus Show Cycle Support
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.
5. When the L2U module has U-bus data bus grant, it drives the read data and the data
phase termination handshakes on the U-bus
6. Release the L-bus.
11.7.6
Show Cycle Support Guidelines
The following are the guidelines for L2U show cycle support:
The L2U module provides address and data for all qualifying L-bus cycles when the
appropriate mode bits are set in the L2U_MCR.
The L2U-module-only provides show cycles L-bus activity that is not targeted for
the U-bus or the L2U module internal registers, regardless of the termination status
of such activity.
The L2U module does not provide show cycle access to any MPC500 special
purpose register.
The L2U does not start a show cycle for an L-bus access that is retried. This decision
to not start the show cycle causes a clock delay before the cycle can be retried, since
the L2U module will have arbitrated away the L-bus immediately on detecting the
show cycle, before the retry information is available.