WEDPN16M64V-XB2X
PRELIMINARY
FIGURE 4 – CAS LATENCY
unwanted commands from being registered during idle or wait
states. Operations already in progress are not affected.
WRITE
The WRITE command is used to initiate a burst write access to an
active row. The value on the BA0, BA1 inputs selects the bank, and
the address provided on inputs A0-8 selects the starting column
location. The value on input A10 determines whether or not AUTO
PRECHARGE is used. IfAUTO PRECHARGE is selected, the row
being accessed will be precharged at the end of the WRITE burst;
ifAUTO PRECHARGE is not selected, the row will remain open for
subsequent accesses. Input data appearing on the DQs is written
to the memory array subject to the DQM input logic level appearing
coincident with the data. If a given DQM signal is registered LOW,
the corresponding data will be written to memory; if the DQM signal
is registered HIGH, the corresponding data inputs will be ignored,
and a WRITE will not be executed to that byte/column location.
LOAD MODE REGISTER
The Mode Register is loaded via inputsA0-11. See Mode Register
heading in the Register Definition section. The LOAD MODE
REGISTER command can only be issued when all banks are
idle, and a subsequent executable command cannot be issued
until tMRD is met.
ACTIVE
The ACTIVE command is used to open (or activate) a row in a
particular bank for a subsequent access. The value on the BA0,
BA1 inputs selects the bank, and the address provided on inputs
A0-A12 selects the row. This row remains active (or open) for
accesses until a PRECHARGE command is issued to that bank. A
PRECHARGE command must be issued before opening a different
row in the same bank.
PRECHARGE
The PRECHARGE command is used to deactivate the open row
in a particular bank or the open row in all banks. The bank(s) will
be available for a subsequent row access a specified time (tRP
)
READ
after the PRECHARGE command is issued. InputA10 determines
whether one or all banks are to be precharged, and in the case
where only one bank is to be precharged, inputs BA0, BA1 select
the bank. Otherwise BA0, BA1 are treated as “Don’t Care.” Once
a bank has been precharged, it is in the idle state and must be
activated prior to any READ or WRITE commands being issued
to that bank.
The READ command is used to initiate a burst read access to an
active row. The value on the BA0, BA1 inputs selects the bank, and
the address provided on inputs A0-8 selects the starting column
location. The value on input A10 determines whether or not AUTO
PRECHARGE is used. IfAUTO 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 data appears on the I/Os subject
to the logic level on the DQM inputs two clocks earlier. If a given
DQM signal was registered HIGH, the corresponding I/Os will be
High-Z two clocks later; if the DQM signal was registered LOW,
the I/Os will provide valid data.
AUTO PRECHARGE
AUTO PRECHARGE is a feature which performs the same
individual-bank PRECHARGE function described above, without
requiring an explicit command. This is accomplished by using
A10 to enable AUTO PRECHARGE in conjunction with a specific
READ or WRITE command. A precharge of the bank/row that is
Microsemi Corporation reserves the right to change products or specifications without notice.
July 2011 © 2011 Microsemi Corporation. All rights reserved.
Rev. 1
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