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6-14 Intel® PXA255 Processor Developer’s Manual
Memory Controller
6.5.3 SDRAM MDREFR Register (MDREFR)
MDREFR, shown in Table 6-5, is a read/write register and contains control bits that refresh both
SDRAM partition pairs. MDREFR also contains control and status bits for SDRAM self-refresh,
SDRAM/SMROM clock divisors, SDRAM/SMROM clocks running, and SDRAM/SMROM
clock-enable pin states. Independent control/status is provided for each of the clock pins
(SDCLK[2:0]) and clock-enable pins (SDCKE[1:0]).
The clock-run bits (K0RUN, K1RUN, and K2RUN) and clock-enable bits (E0PIN and E1PIN)
provide software control of SDRAM and Synchronous Static Memory low-power modes. When
the clock-run bits and clock-enable bits are cleared, the corresponding memory is inaccessible.
Automatic power-down, enabled by the APD bit, is an mechanism for minimizing power
consumption in the processor SDCLK pin drivers and/or the SDRAM/Synchronous Static Memory
devices. A latency penalty of one memory cycle is incurred when SDCLK and SDCKE are
restarted between non-consecutive SDRAM/Synchronous Static Memory transfers.
The following conditions determine whether SDRAM refreshes occur.
• No refreshes are sent to SDRAM when the refresh counter is cleared to zero.
• If a single transaction to a disabled SDRAM partition is requested, a refresh to all four
partitions is performed.
• If all four SDRAM partitions are disabled, the refresh counter is disabled.
• If the clock frequency is changed, the register must be rewritten, even if the value has not
changed. This results in a refresh and the refresh counter being reset to the next refresh
interval.
Table 6-4. MDMRSLP Register Bit Definitions
0X4800 0058 MDMRSLP
Bit
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
MDLPEN2
MDMRSLP2
MDLPEN0
MDMRSLP0
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Bits Name Description
31 MDLPEN2
ENABLE BIT FOR LOW POWER MRS VALUE FOR PARTITION PAIR 2/3:
0 – Disable low power MRS for Partition Pair 2/3
1 – Enable low power MRS for Partition Pair 2/3
30:16 MDMRSLP2
LOW POWER MRS VALUE TO BE WRITTEN TO SDRAM FOR
PARTITION PAIR 2/3
15 MDLPEN0
Enable bit for low power MRS value for Partition Pair 0/1.
0 – Disable low power MRS for Partition Pair 0/1
1 – Enable low power MRS for Partition Pair 0/1
14:0 MDMRSLP0
LOW POWER MRS VALUE TO BE WRITTEN TO SDRAM FOR
PARTITION PAIR 0/1