W3H32M64EA-XSBX
ADVANCED
FIGURE 11 – READ COMMAND
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.
CK#
CK
CKE
CS#
READ OPERATION
RAS#
CAS#
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.
WE#
Col
ADDRESS
During READ bursts, the valid data-out element from the starting
column address will be available READ latency (RL) clocks later.
RL is defined as the sum of AL and CL; RL = AL + CL. The value
forAL 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#).
ENABLE
A10
AUTO PRECHARGE
BANK ADDRESS
DISABLE
Bank
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).
DON’T CARE
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 flow of data.
The first 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 first READ command, where x equals BL/ 2 cycles.
Microsemi Corporation reserves the right to change products or specifications without notice.
August 2011 © 2011 Microsemi Corporation. All rights reserved.
Rev.1
16
Microsemi Corporation • (602) 437-1520 • www.microsemi.com
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