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White Electronic Designs Corporation (602) 437-1520 www.whiteedc.com
White Electronic Designs
February 2010 2010 White Electronic Designs Corp. All rights reserved
Rev. 0
ADVANCED
White Electronic Designs Corp. reserves the right to change products or specications without notice.
W3H32M64EA-XSBX
READ COMMAND
The READ command is used to initiate a burst read access
to an active row. The value on the bank address inputs
selects the bank, and the address provided on inputs
A0–i (where i = A9) selects the starting column location.
The value on input A10 determines whether or not auto
precharge is used. If auto precharge is selected, the row
being accessed will be precharged at the end of the READ
burst; if auto precharge is not selected, the row will remain
open for subsequent accesses.
READ OPERATION
READ bursts are initiated with a READ command. The
starting column and bank addresses are provided with the
READ command and auto precharge is either enabled or
disabled for that burst access. If auto precharge is enabled,
the row being accessed is automatically precharged at the
completion of the burst. If auto precharge is disabled, the
row will be left open after the completion of the burst.
During READ bursts, the valid data-out element from the
starting column address will be available READ latency
(RL) clocks later. RL is dened as the sum of AL and CL;
RL = AL + CL. The value for AL and CL are programmable
via the MR and EMR commands, respectively. Each
subsequent data-out element will be valid nominally at
the next positive or negative clock edge (i.e., at the next
crossing of CK and CK#).
DQS/DQS# is driven by the DDR2 SDRAM along with
output data. The initial LOW state on DQS and HIGH state
on DQS# is known as the read preamble (tRPRE). The
LOW state on DQS and HIGH state on DQS# coincident
with the last data-out element is known as the read
postamble (tRPST).
Upon completion of a burst, assuming no other commands
have been initiated, the DQ will go High-Z.
Data from any READ burst may be concatenated with
data from a subsequent READ command to provide a
continuous ow of data. The rst data element from the
new burst follows the last element of a completed burst.
The new READ command should be issued x cycles after
the rst READ command, where x equals BL / 2 cycles.
FIGURE 11 – READ COMMAND
DON’T CARE
CK
CK#
CS#
RAS#
CAS#
WE#
CKE
Col
Bank
ADDRESS
BANK ADDRESS
AUTO PRECHARGE
ENABLE
DISABLE
A10