Self-Refresh Mode: Some DRAM devices have a self-refresh function. After the SRFMD bit is
set to 1 in RFSHCR, when a transition to software standby mode occurs, the
CAS
and
RAS
outputs go low in that order so that the DRAM self-refresh function can be used. On exit from
software standby mode, the
CAS
and
RAS
outputs both go high.
Table 7-7 shows the pin states in software standby mode. Figure 7-6 shows the signal output
timing.
Table 7-7 Pin States in Software Standby Mode (1) (PSRAME = 0, DRAME = 1)
Software Standby Mode
SRFMD = 0
SRFMD = 1 (self-refresh mode)
Signal
CAS/
WE
= 0
CAS/
WE
= 1
CAS/
WE
= 0
CAS/
WE
= 1
HWR
High-impedance
High-impedance
High
Low
LWR
High-impedance
High-impedance
High
Low
RD
High-impedance
High-impedance
Low
High
CS
3
High
High
Low
Low
RFSH
High
High
Low
Low
162
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