
Chapter 9. System Interface Operation
9-9
60x Bus Protocol
Figure 9-3. Overlapping Tenures on the MPC7400 Bus for a Single-Beat Transfer
The basic functions of the address and data tenures are as follows:
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Address tenure
Arbitration: During arbitration, address bus arbitration signals are used to gain
mastership of the address bus.
Transfer: After the MPC7400 is the address bus master, it transfers the address
on the address bus. The address signals and the transfer attribute signals control
the address transfer. The address parity signals ensure the integrity of the address
transfer.
Termination: After the address transfer, the system signals that the address tenure
is complete or that it must be repeated.
Data tenure
Arbitration: To begin the data tenure, the MPC7400 arbitrates for mastership of
the data bus.
Transfer: After the MPC7400 is the data bus master, it samples the data bus for
read operations or drives the data bus for write operations. The data parity signals
ensure the integrity of the data transfer.
Termination: Data termination signals are required after each data beat in a data
transfer. Note that in a single-beat transaction, the data termination signals also
indicate the end of the tenure, while in burst accesses, the data termination
signals apply to individual beats and indicate the end of the tenure only after the
Tnal data beat.
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The MPC7400 generates an address-only bus transfer during the execution of the
dcbz
,
sync
, and
eieio
instructions and in some instances of the
dcbf
and
dcbst
instructions (when
they do not result in a hit of modiTed data in the cache). Additionally, the MPC7400s retry
capability provides an efTcient snooping protocol for systems with multiple memory
systems (including caches) that must remain coherent.
Address Tenure
Data Tenure
Independent Address and Data
Arbitration
Transfer
Termination
Arbitration
Single-beat Transfer
Termination