mcf5407 Freescale Semiconductor, Inc, mcf5407 Datasheet - Page 299

• Manufacturer Part Number: mcf5407
• Description: Mcf5407 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

11.4.4.5 Auto-Refresh Operation
The DRAM controller is equipped with a refresh counter and control. This logic is
responsible for providing timing and control to refresh the SDRAM. Once the refresh
counter is set, and refresh is enabled, the counter counts to zero. At this time, an internal
refresh request flag is set and the counter begins counting down again. The DRAM
controller completes any active burst operation and then performs a
DRAM controller then initiates a refresh cycle and clears the refresh request flag. This
refresh cycle includes a delay from any precharge to the auto-refresh command, the
auto-refresh command, and then a delay until any
access initiated during the auto-refresh cycle is delayed until the cycle is completed.
Figure 11-22 shows the auto-refresh timing. In this case, there is an SDRAM access when
the refresh request becomes active. The request is delayed by the precharge to
programmed into the active SDRAM bank by the CAS bits. The
generated and the delay required by DCR[RTIM] is inserted before the next
command is generated. In this example, the next bus cycle is initiated, but does not generate
an SDRAM access until T
command, it is passed to both blocks of external SDRAM.
RAS[0] or [1]
Figure 11-21. Synchronous, Continuous Page-Mode Access—Read after Write
CAS[3:0]
DRAMW
D[31:0]
A[31:0]
CLKIN
SRAS
SCAS
ACTV
t
RCD
Row
Chapter 11. Synchronous/Asynchronous DRAM Controller Module
= 3
RC
NOP
is finished. Because both chip selects are active during the
WRITE
Column
NOP
ACTV
READ
command is allowed. Any SDRAM
Column
t
CASL
NOP
= 3
REF
NOP
Synchronous Operation
PALL
command is then
operation. The
NOP
t
EP
ACTV
PALL
delay
ACTV
11-31
REF