
10-6
MPC565/MPC566 Reference Manual
MOTOROLA
Memory Controller Architecture
NOTE
When an external master accesses a slave on the bus, the
internal AT[0:2] lines reaching the memory controller are
forced to 100.
10.2.5 Burst Support
The memory controller supports burst accesses of external burstable memory. To enable
bursts, clear the burst inhibit (BI) bit in the appropriate base register. Burst support is for
read only.
Bursts can be four or eight beats depending on the value of the BURST_EN bit in the
SIUMCR register and the BL bit in the BR register. That is, the memory controller executes
up to eight one-word accesses, but when a modulo eight limit is reached, the burst is
terminated (even if fewer than eight words have been accessed).
When the SIU initiates a burst access, if no match is found in any of the memory
controller’s regions then a burst access is initiated to the external bus. The termination of
each beat for this access is externally controlled.
To support different types of memory devices, the memory controller supports two types of
timing for the BDIP signal: normal and late.
NOTE
The BDIP pin itself is controlled by the external bus interface
If the memory controller is used to support an external master accessing an external device
with bursts, the BDIP input pin is used to indicate to the memory controller when the burst
is terminated.
10.2.6 Reduced Data Setup Time
In order to meet timing requirements when interfacing to external memories, the data setup
time can be reduced. This mode can be selected by programming the BRx registers. Thus
there is flexibility in how each region can be configured to operate. The operation mode
will be determined dynamically according to a particular access type. This means that for
a memory region with the reduced setup time mode enabled, the mode will automatically
switch to disabled when there is no requirement for the reduced setup time, (e.g., a back to
back load store access). For a new access with burst length more than 1, the operation mode
will be automatically switched back to the reduced setup time mode.