Motorola ColdFire MCF5281 - Manual (Page 288)

Synchronous DRAM Controller Module
15-16 Freescale Semiconductor
Figure 15-8 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 ACTV delay programmed into the active
SDRAM bank by the CAS bits. The REF command is then generated and the delay required by
DCR[RTIM] is inserted before the next ACTV command is generated. In this example, the next bus cycle
is initiated, but does not generate an SDRAM access until T
RC
is finished. Because both chip selects are
active during the REF command, it is passed to both blocks of external SDRAM.
Figure 15-8. Auto-Refresh Operation
15.2.3.6 Self-Refresh Operation
Self-refresh is a method of allowing the SDRAM to enter into a low-power state, while at the same time
to perform an internal refresh operation and to maintain the integrity of the data stored in the SDRAM. The
DRAM controller supports self-refresh with DCR[IS]. When IS is set, the
SELF command is sent to the
SDRAM. When IS is cleared, the SELFX command is sent to the DRAM controller. Figure 15-9 shows the
self-refresh operation.
A[23:0]
SRAS
SCAS
DRAMW
PALL
SDRAM_CS[0] or [1]
REF ACTV
t
RCD
= 2
t
RC
= 6
CLKOUT
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3