MPC555
/
MPC556
EXTERNAL BUS INTERFACE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
9-14
Figure 9-9 Single Beat Basic Write Cycle Timing, One Wait State
9.5.2.3 Single Beat Flow with Small Port Size
The general case of single beat transfers assumes that the external memory has a 32-
bit port size. The MPC555
/ MPC556 provides an effective mechanism for interfacing
with 16-bit and 8-bit port size memories, allowing transfers to these devices when they
are controlled by the internal memory controller.
In this case, the MPC555
/ MPC556 attempts to initiate a transfer as in the normal
case. If the bus interface receives a small port size (16 or 8 bits) indication before the
transfer acknowledge to the first beat (through the internal memory controller), the
MCU initiates successive transactions until the completion of the data transfer. Note
that all the transactions initiated to complete the data transfer are considered to be part
of an atomic transaction, so the MCU does not allow other unrelated master accesses
CLKOUT
ADDR[0:31]
TS
BR
BG
BB
Data
TA
RD/WR
Receive bus grant and bus busy negated
Assert BB, drive address and assert TS
Data is sampled
BURST, BDIP
TSIZ[0:1]
Wait state
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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