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(2) Self-Refresh
One of the DRAM standby modes is the self-refresh mode (battery backup mode), in which the
DRAM generates its own refresh timing and refresh address.
To select self-refresh, set the RFSHE bit and RMODE bits of the DRAMCR to 1. Next, execute a
SLEEP instruction to make a transition to software standby mode. As shown in Figure 7-29, the
CAS and RAS signals are output and the DRAM enters self-refresh mode.
When you exit software standby mode, the RMODE bit is cleared to 0 and self-refresh mode is
exited.
When making a transition to software standby mode, self-refresh mode starts after a CBR refresh,
providing there is a CBR refresh request. CBR refresh requests occurring immediately before
entering software standby mode are cleared on completion of the self-refresh when the software
standby mode is exited.
Software standby
T
T
T
Rp
Rcr
Rc3
ø
CSn (RAS)
CAS, LCAS
HWR (WE)
High level
Note: n= 2 to 5
Figure 7-29 Self-Refresh Timing
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