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MPC7400 RISC Microprocessor Users Manual
Signal Groupings
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Transfer attributeThese signals provide information about the type of transfer,
such as the transfer size and whether the transaction is bursted, write-through, or
cache-inhibited.
Address transfer terminationThese signals are used to acknowledge the end of the
address phase of the transaction. They also indicate whether a condition exists that
requires the address phase to be repeated.
Data arbitrationThe MPC7400 uses these signals to arbitrate for data bus
mastership.
Data transferThese signals, which consist of the data bus and data parity, are used
to transfer the data and to ensure the integrity of the transfer.
Data transfer terminationData termination signals are required after each data
beat in a data transfer. In a single-beat transaction, the data termination signals also
indicate the end of the tenure. In burst accesses, the data termination signals apply
to individual beats and indicate the end of the tenure only after the Tnal data beat.
The data termination signals also indicate whether a condition exists that requires
the data phase to be repeated.
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In addition there are many other signals on the MPC7400 that control and affect other
aspects of the device, aside from the bus protocol as follows:
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L2 cache address/dataThe MPC7400 has separate address and data buses for
accessing the L2 cache.
L2 cache clock/controlThese signals provide clocking and control for the L2
cache.
Interrupts/resetsThese signals include the external interrupt signal, checkstop
signals, and both soft reset and hard reset signals. They are used to interrupt and,
under various conditions, to reset the processor.
Processor status and controlThese signals are used to set the reservation
coherency bit, and enable the time base and other functions. They are also used in
conjunction with such resources as secondary caches and the time base facility.
Clock controlThese signals determine the system clock frequency. They are also
used to synchronize multiprocessor systems.
Test interfaceThe JTAG (IEEE 1149.1a-1993) interface and the common on-chip
processor (COP) unit provide a serial interface to the system for performing
board-level boundary-scan interconnect tests.
Voltage select These signals control the voltages of the L2 interface and the rest
of the device.
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