
4-6
MPC106 PCIB/MC User's Manual
MOTOROLA
4.2 Processor Bus Protocol Overview
60x bus accesses are divided into address and data tenures. Each tenure has three phases—
bus arbitration, transfer, and termination. Figure 4-4 shows that the address and data tenures
are distinct from one another and that both consist of three phases—arbitration, transfer,
and termination. Address and data tenures are independent (indicated in Figure 4-4 by the
fact that the data tenure begins before the address tenure ends), which allows split-bus
transactions to be implemented at the system level in multiprocessor systems. Figure 4-4
demonstrates a data transfer that consists of a single-beat transfer of as many as 64 bits.
Figure 4-4. Overlapping Tenures on the 60x Bus for a Single-Beat Transfer
The basic functions of the address and data tenures are as follows:
Address tenure
— Arbitration: During arbitration, address bus arbitration signals are used to gain
mastership of the address bus.
— Transfer: After a bus master is granted mastership of the address bus, it transfers
the address. The address signals and the transfer attribute signals control 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: Following the initiation of the address tenure, the bus master
arbitrates for mastership of the data bus.
— Transfer: After the bus master is granted mastership of the data bus, it samples
the data bus for read operations or drives the data bus for write operations.
— 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
final data beat.
ARBITRATION
TRANSFER
TERMINATION
ADDRESS TENURE
ARBITRATION
SINGLE-BEAT TRANSFER
TERMINATION
DATA TENURE
INDEPENDENT ADDRESS AND DATA