AS4SD16M72PBG-s/IT,ET,XT
16M x 72, SDR SDRAM, 3.3v Core/ 3.3v IO
Specifies the type of burst (sequential or interleaved), M4-M6
specify the CAS latency, M7 and M8 specify the operating
mode, M9 specifies the WRITE BURST mode and M10,
M11 are reserved for future use. Address A12 (M12) is
undefined but should be driven LOW during loading of the
MODE REGISTER.
The MODE REGISTER must be loaded when all banks are
idle, and the controller must wait the specified time before
initiating the subsequent operation. Violating either of these
requirements will result in unspecified operation.
N + m. The DQs will start driving as a result of the clock
edge one cycle earlier (n + m - 1), and provided that the
relevant access times are met, the data will be valid by
clock edge n + m. For example, assuming that the clock
cycle time is such that all relevant access times are met, If
a READ command is registered at T0 and the latency is
programmed to two clocks, the DQs will be valid by T2.
Reserved states should not be used as unknown operation
or incompatibility with future versions may result.
Operating Mode
Burst Length
READ and WRITE accesses to the SDRAM are burst
oriented, with the burst length being programmable. The
burst length determines the maximum number of column
locations that can be accessed for a given READ or WRITE
command. Burst lengths of 1,2,4 and 8 locations are available
for both the sequential and the interleaved burst types, and a
full page burst is available for the sequential burst mode. The
full-page burst is used in conjunction with the BURST
TERMINATE command to generate arbitrary burst lengths.
Reserved states should not be used, aas unknown operation or
incompatibility with future versions may result.
When a READ or WRITE command is issued, a block of
columns equal to the burst length is effectively selected. All
accesses for that burst will wrap within this block, meaning
that the burst will wrap within the block if a boundary is
reached. The block is uniquely selected by A2-A8 (each x16)
when the burst length is set to four; and by A3-A8 (each x16)
when the burst length is set to eight. The remaining (least
significant) address bit(s) is (are) used to select the starting
location within the block. Full-page bursts wrap within the
page if the boundary is reached.
The normal operating mode is selected by setting M7 and
M8 to zero; the other combinations of values for M7 and
M8 are reserved for future use and/or test modes. The
programmed burst length applies to both READ and
WRITE bursts.
Test Modes and reserved states should not be used
because unknown operation or incompatibility with future
version may result.
Write Burst Mode
When M9=0, the burst length programmed via M0-M2
applies to both READ and WRITE bursts; when M9=1,
the programmed burst length applies to READ bursts, but
WRITE accesses are single-location (non-burst) accesses.
Command Inhibit
The COMMAND INHIBIT function prevents new
commands from being executed by the SDRAM,
regardless of whether the CLK signal is enabled. The
SDRAM is effectively deselected. Operations already in
progress are not affected.
CAS Latency
The CAS latency is the delay, in clock cycles, between the
registration of a READ command and the availability of first
valid data presented on the Output bus (DQ0-DQ79). The
latency can be set to two or three clocks.
If a READ command is registered at clock edge n, and the
latency is m clocks, the data will be available by clock edge
Austin Semiconductor, Inc.
No Operation (NOP)
The NO OPERATION (NOP) command is used to
perform a NOP to an SDRAM which is selected (CS\ is
LOW). This prevents unwanted commands from being
registered during IDLE or WAIT states. Operations
already in progress are not affected.
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