W948D6FBHX5E-TR Datasheet, PDF (10/60 Pages) Winbond – 256Mb Mobile LPDDR

W948D6FB / W948D2FB
6. FUNCTION DESCRIPTION
6.1 Initialization
256Mb Mobile LPDDR
LPDDR SDRAM must be powered up and initialized in a predefined manner. Operations procedures other than
those specified may result in undefined operation. If there is any interruption to the device power, the initialization
routine should be followed. The steps to be followed for device initialization are listed below.
The Mode Register and Extended Mode Register do not have default values. If they are not programmed during the
initialization sequence, it may lead to unspecified operation. The clock stop feature is not available until the device
has been properly initialized from Step 1 through 11.
 Step 1: Provide power, the device core power (VDD) and the device I/O power (VDDQ) must be brought up
simultaneously to prevent device latch-up. Although not required, it is recommended that VDD and VDDQ
are from the same power source. Also Assert and hold Clock Enable (CKE) to a LVCMOS logic high level.
 Step 2: Once the system has established consistent device power and CKE is driven high, it is safe to apply
stable clock.
 Step 3: There must be at least 200μs of valid clocks before any command may be given to the DRAM. During this
time NOP or DESELECT commands must be issued on the command bus.
 Step 4: Issue a PRECHARGE ALL command.
 Step 5: Provide NOPs or DESELECT commands for at least tRP time.
 Step 6: Issue an AUTO REFRESH command followed by NOPs or DESELECT command for at least tRFC time.
Issue the second AUTO REFRESH command followed by NOPs or DESELECT command for at least
tRFC time. Note as part of the initialization sequence there must be two Auto Refresh commands issued.
The typical flow is to issue them at Step 6, but they may also be issued between steps 10 and 11.
 Step 7: Using the MRS command, program the base mode register. Set the desired operation modes.
 Step 8: Provide NOPs or DESELECT commands for at least tMRD time.
 Step 9: Using the MRS command, program the extended mode register for the desired operating modes. Note the
order of the base and extended mode register programmed is not important.
 Step 10: Provide NOP or DESELECT commands for at least tMRD time.
 Step 11: The DRAM has been properly initialized and is ready for any valid command.
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Publication Release Date : Oct, 15, 2012
Revision : A01-004