External Bus Interface
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
9-37
9.5.8
Address Transfer Phase Signals
Address transfer phase signals include the following:
•
Transfer start
•
Address bus
•
Transfer attributes
Transfer attributes signals include RD/WR, BURST, TSIZ[0:1], AT[0:3], STS, and BDIP. With the
exception of the BDIP, these signals are available at the same time as the address bus.
9.5.8.1
Transfer Start
This signal (TS) indicates the beginning of a transaction on the bus addressing a slave device. This signal
should be asserted by a master only after the ownership of the bus was granted by the arbitration protocol.
This signal is asserted for the first cycle of the transaction only and is negated in successive clock cycles
until the end of the transaction. The master should three-state this signal when it relinquishes the bus to
avoid contention between two or more masters in this line. This situation indicates that an external pull-up
resistor should be connected to the TS signal to avoid having a slave recognize this signal as asserted when
no master drives it. Refer to
9.5.8.2
Address Bus
The address bus consists of 32 bits, with ADDR0 the most significant bit and ADDR31 the least significant
bit. Only 24 bits (ADDR[8:31]) are available external to the MPC561/MPC563. The bus is
byte-addressable, so each address can address one or more bytes. The address and its attributes are driven
on the bus with the transfer start signal and kept valid until the bus master receives the transfer
acknowledge signal from the slave. To distinguish the individual byte, the slave device must observe the
TSIZ signals.
9.5.8.3
Read/Write
A high value on the RD/WR line indicates a read access. A low value indicates a write access.
9.5.8.4
Burst Indicator
BURST is driven by the bus master at the beginning of the bus cycle along with the address to indicate that
the transfer is a burst transfer.
The MPC561/MPC563 supports a non-wrapping, 8-beat maximum (with 32-bit port), critical word first
burst type. The maximum burst size is 32 bytes. For a 16-bit port, the burst includes 16 beats. For an 8-bit
port, the burst includes 32 beats at most.
NOTE
8- and 16-bit ports must be controlled by the memory controller.
The actual size of the burst is determined by the address of the starting word of the burst. Refer to
and
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
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...