External Bus Interface
MPC561/MPC563 Reference Manual, Rev. 1.2
9-32
Freescale Semiconductor
lists the patterns of the data transfer for write cycles when the MPC561/MPC563 initiates an
access.
Note:
“—” denotes a byte not driven during that write cycle.
9.5.7
Arbitration Phase
The external bus design provides for a single bus master at any one time, either the MPC561/MPC563 or
an external device. One or more of the external devices on the bus can have the capability of becoming bus
master for the external bus. Bus arbitration may be handled either by an external central bus arbiter or by
the internal on-chip arbiter. In the latter case, the system is optimized for one external bus master besides
the MPC561/MPC563. The arbitration configuration (external or internal) is set at system reset.
Each bus master must have bus request (BR), bus grant (BG), and bus busy (BB) signals. The device that
needs the bus asserts BR. The device then waits for the arbiter to assert BG. In addition, the new master
must look at BB to ensure that no other master is driving the bus before it can assert BB to assume
ownership of the bus. Any time the arbiter has taken the bus grant away from the master and the master
wants to execute a new cycle, the master must re-arbitrate before a new cycle can be executed. The
MPC561/MPC563, however, guarantees data coherency for access to a small port size and for decomposed
bursts. This means that the MPC561/MPC563 will not release the bus before the completion of the
transactions that are considered atomic.
describes the basic protocol for bus arbitration.
Table 9-3. Data Bus Contents for Write Cycles
Transfer
Size
TSIZE[0:1]
Address
External Data Bus Pattern
ADDR
[30:31]
DATA
[0:7]
DATA
[8:15]
DATA
[16:23]
DATA
[24:31]
Byte
01
00
OP0
—
—
—
01
01
OP1
OP1
—
—
01
10
OP2
—
OP2
—
01
11
OP3
OP3
—
OP3
Half-word
10
00
OP0
OP1
—
—
10
10
OP2
OP3
OP2
OP3
Word
00
00
OP0
OP1
OP2
OP3
Summary of Contents for MPC561
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Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...