Memory Controller Power-Down - NEC µPD72257 Preliminary User's Manual

Chapter 9

9.5 Memory Controller Power-Down

Figure 9-13
312
The SDRAM can be put into power-down mode to save power. This is executed
by setting MEMSCTRL.PWDM = 1.
The figure below illustrates the command sequence issued by the SDRAM
controller to initiate, maintain, and exit power-down mode.
Exit
power-down
Power-down command sequence
The Memory Controller can be set into power-down mode by setting
MEMSCTRL.PWDM = 1.
When in SDRAM power-down mode, the Memory Controller keeps switching the
device back and forth between power-down and refresh mode. It remains in
power-down for a refresh period of time (defined by MEMSREFR.TREF), then
comes out of power-down and does a single-row refresh. Afterwards it again goes
into power-down mode.
Preliminary User's Manual S19203EE1V3UM00
External Memory Interface Controller
MEMSCTRL.PWDM = 1
Power-down
MDCKE low
MDCKE high
NOP
Refresh single row
or
execute read/write access
MEMSCTRL.PWDM = 0
NOP
Ready for data transfer
MEMSREFR.
TREF
Temporary exit
from power-down
for refresh or
memory read/write
access