SDRAM
AS4SD4M16
Austin Semiconductor, Inc.
COMMAND INHIBIT
The COMMAND INHIBIT function prevents new
WRITE
The WRITE command is used to initiate a burst write
commands from being executed by the SDRAM, regardless of access to an active row. The value on the BA0, BA1 inputs
whether the CLK signal is enabled. The SDRAM is effectively selects the bank, and the address provided on inputs A0-A7
deselected. Operations already in progress are not affected.
(x16) 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
NO OPERATION (NOP)
The NO OPERATION (NOP) command is used to per- be precharged at the end of the WRITE burst; if AUTO
form a NOP to an SDRAM which is selected (CS\ is LOW). This PRECHARGE is not selected, the row will remain open for sub-
prevents unwanted commands from being registered during sequent accesses. Input data appearing on the DQs is written
idle or wait states. Operations already in progress are not af- to the memory array subject to the DQM input logic level ap-
fected.
pearing 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 correspond-
LOAD MODE REGISTER
The Mode Register is loaded via inputs A0-A11. See ing data inputs will be ignored, and a WRITE will not be ex-
Mode Register heading in the Register Definition section. The ecuted to that byte/column location.
LOAD MODE REGISTER command can only be issued when
all banks are idle, and a subsequent executable command can- PRECHARGE
not be issued until tMRD is met.
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 speci-
ACTIVE
The ACTIVE command is used to open (or activate) a
fied time (tRP) after the PRECHARGE command is issued. Input
A10 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 com-
mands being issued to that bank.
row in a particular bank for a subsequent access. The value on
the BA0, BA1 inputs selects the bank, and the address pro-
vided on inputs A0-A11 selects the row. This row remains ac-
tive (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.
READ
AUTO PRECHARGE
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-A7
(x16) 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 sub-
sequent accesses. Read data appears on the DQs subject to
the logic level on the DQM inputs two clocks earlier. If a given
DQM signal was registered HIGH, the corresponding DQs will
be High-Z two clocks later; if the DQM signal was registered
LOW, the DQs will provide valid data.
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 addressed with the READ or WRITE com-
mand is automatically performed upon completion of the READ
or WRITE burst, except in the full-page burst mode, where
AUTO PRECHARGE does not apply. AUTO PRECHARGE is
nonpersistent in that it is either enabled or disabled for each
individual READ or WRITE command.
AUTO PRECHARGE ensures that the precharge is
initiated at the earliest valid stage within a burst. The user must
not issue another command to the same bank until the precharge
time (tRP) is completed. This is determined as if an explicit
PRECHARGE command was issued at the earliest possible time,
as described for each burst type in the Operation section of this
data sheet.
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
AS4SD4M16
Rev. 2.1 6/05
10
AUSTIN [ AUSTIN SEMICONDUCTOR ]
