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The following conditions must be observed when the self-refresh function is used:
• When burst access is selected, RAS up mode must be selected before executing a SLEEP
instruction in order to enter software standby mode. Therefore, if RAS down mode has been
selected, the RDM bit in DRCRA must be cleared to 0 and RAS up mode selected before
executing the SLEEP instruction. Select RAS down mode again after exiting software standby
mode.
• The instruction immediately following a SLEEP instruction must not be located in an area
designated as DRAM space.
The self-refresh function will not work properly unless the above conditions are observed.
φ
Address bus
CS
(RAS)
n
PB4(UCAS)
PB5(LCAS)
RD(WE)
RFSH
Refresh Signal (RFSH): A refresh signal (RFSH) that transmits a refresh cycle off-chip can be
output by setting the RFSHE bit to 1 in DRCRA. RFSH output timing is shown in figures 6.26,
6.27, and 6.28.
6.5.12
Examples of Use
Examples of DRAM connection and program setup procedures are shown below. When the
DRAM interface is used, check the DRAM device characteristics and choose the most appropriate
method of use for that device.
160
Software standby
mode
High-impedance
Figure 6.28 Self-Refresh Timing (CSEL = 0)
Oscillation stabilization
time
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