Motorola MPC533 Reference Manual page 420

Modes Of Operation
• Slave mode enables an external master to access any internal bus slave while the
RCPU is fully operational. The L2U transfers load/store accesses from the RCPU to
the U-bus and the read/write accesses by the U-bus master to the L-bus.
In addition to the bus protocol translation, the L2U supports other functions such as show
cycles, data memory protection, and MPC500 reservation protocol.
When a load to or store from the U-bus resource is issued by the RCPU, it is compared
against the DMPU region access (address and attribute) comparators. If none of the access
attributes are violated, the access is directed to the U-bus by the L2U module. If the DMPU
detects an access violation, it informs the error status to the master initiating the cycle.
When show cycles are enabled, accesses to all of the L-bus resources by the RCPU are
made visible on the U-bus side by the L2U.
The L2U is responsible for handling the effects of reservations on the L-bus and the U-bus.
For the L-bus and the U-bus, the L2U detects reservation losses and updates the RCPU core
with the reservation status.
11.4.2 Reset Operation
While hard or soft reset is asserted on the U-bus, the L2U asserts the corresponding L-bus
reset signals. Upon soft reset assertion, the L2U goes to an idle state and all pending
accesses are ignored. Additionally, the L2U module control registers are not initialized on
soft reset, keeping the system configuration unchanged.
Upon assertion of hard reset, the L2U control registers are initialized to their reset states.
The L2U also drives the reset configuration word from the U-bus to the L-bus upon hard
reset.
11.4.3 Peripheral Mode
In the peripheral mode of operation the RCPU is shut down and an alternative master on
the external bus can perform accesses to any internal bus (U-bus and L-bus) slave.
The external master can also access the internal MPC500 special registers that are located
in the L2U module. In order to access one of these MPC500 registers the EMCR[CONT]
bit in the USIU must be cleared.
11.4.4 Factory Test Mode
Factory test mode is a special mode of operation that allows access to the internal modules
for testing. This mode is not intended for general use and is not supported for normal
applications.
11-4
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
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