HD6417021 Hitachi Semiconductor, HD6417021 Datasheet - Page 166
HD6417021
Manufacturer Part Number
HD6417021
Description
SuperH RISC engine
Manufacturer
Hitachi Semiconductor
Datasheet
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enter the self-refresh mode when the CAS and RAS signals are output as shown in figure 8.31. See
section 20.3.3, Bus Timing, for details. The DRAM self-refresh mode is cleared when the
RMODE bit in the RCR is cleared to 0 (figure 8.31). The RFSHE bit should be left at 1 when this
is done. Some DRAM vendors recommend that after exiting the self-refresh mode, all row
addresses should be refreshed again. This can be done using the BCR’s CBR refresh function to
set all row addresses for refresh in software.
To access a DRAM area in the self-refresh mode, clear the RMODE bit to 0 and exit the self-
refresh mode.
The LSI can be kept in the self-refresh state and shifted to standby mode by setting it to self-
refresh mode, setting the standby bit (SBY) of the standby control register (SBYCR) to 1, and then
executing a SLEEP instruction.
Refresh Requests and Bus Cycle Requests: When a CAS-before-RAS refresh or self-refresh is
requested during bus cycle execution, parallel execution is sometimes possible. Table 8.10
describes operation when the refresh and bus cycle are in contention.
150 HITACHI
RAS
CAS
CK
T
Rp
Figure 8.31 Output Timing of Self-Refresh Signal
T
Rr
T
Rc
T
Rcc
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