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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, irrespective 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.
• The L2U module does not show cycle any L-bus activity that is aborted.
• The L2U module does not access the U-bus if the USIU inhibits show cycle activity
on the U-bus.
• The L2U does not provide show cycle for any L-bus addresses that fall in the L-bus
CALRAM address space if the CALRAM protection [SP] bit is set in the
L2U_MCR.
Table 11-4 summarizes the L2U show cycle support.
Case
Destination
1
L-bus Slave
2
L2U
3
U-bus/E-bus
4
L-bus slave
5
L-bus slave
1
L-bus slave includes all address in the L-bus address space.
2
X indicates don't care conditions.
3
There will be a 1-clock turnaround because the L-bus retry information is not available in time to
negate the L-bus arbitration.
4
L2U indicates L2U registers.
5
U-bus/E-bus refers to all destinations through the L2U interface.
MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Table 11-4. L2U Show Cycle Support Chart
LB AACK
LB ABORT
1
No
4
X
5
X
1
Yes
1
Yes
Chapter 11. L-Bus to U-Bus Interface (L2U)
Comments
2
X
Not show cycled
[Cycle will be retried one clock later]
X
Not show cycled
X
Not show cycled
No
Show cycled
Yes
Not show cycled
[L-bus will be released next clock]
L-Bus Show Cycle Support
3
11-13
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