256MB / 512MB (x64)
168-PIN SDRAM DIMMs
MAND INHIBIT or NOP Starting at some point during
.
this 100µs period and continuing at least through the
end of this period, COMMAND INHIBIT or NOP com-
mands should be applied.
Once the 100µs delay has been satisfied with at least
one COMMAND INHIBIT or NOP command having
been applied, a PRECHARGE command should be
applied. All device banks must then be precharged,
thereby placing the device in the all banks idle state.
Once in the idle state, two AUTO REFRESH cycles
must be performed. After the AUTO REFRESH cycles
are complete, the SDRAM is ready for mode register
programming. Because the mode register will power
up in an unknown state, it should be loaded prior to
applying any operational command.
Reserved states should not be used, as 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 take place within
this block, meaning that the burst will wrap within the
block if a boundary is reached, as shown in the Burst
Definition Table. The block is uniquely selected by A1–
A9 when the burst length is set to two; A2–A9 when the
burst length is set to four; and by A3–A9 when the burst
length is set to eight. The remaining (least significant)
address bit(s) is (are) used to select the starting loca-
tion within the block. Full-page bursts wrap within the
page if the boundary is reached, as shown in Table 7,
Mode Register Definition
The mode register is used to define the specific
mode of operation of the SDRAM. This definition
includes the selection of a burst length, a burst type, a
CAS latency, an operating mode and a write burst
mode, as shown in Figure 5, Mode Register Definition
via the LOAD MODE REGISTER command and will
retain the stored information until it is programmed
again or the device loses power.
Mode register bits M0–M2 specify the burst length,
M3 specifies the type of burst (sequential or inter-
leaved), M4–M6 specify the CAS latency, M7 and M8
specify the operating mode, M9 specifies the write
burst mode, and M10 and M11 are reserved for future
use.
The mode register must be loaded when all device
banks are idle, and the controller must wait the speci-
fied time before initiating the subsequent operation.
Violating either of these requirements will result in
unspecified operation.
Burst Type
Accesses within a given burst may be programmed
to be either sequential or interleaved; this is referred to
as the burst type and is selected via bit M3.
The ordering of the accesses within a burst is deter-
mined by the burst length, the burst type, and the
starting column adress, as shown in Table 7, Burst Def-
Burst Length
Read and write accesses to the SDRAM are burst ori-
ented, with the burst length being programmable, as
shown in Figure 5, Mode Register Definition Diagram,
number of column locations that can be accessed for a
given READ or WRITE command. Burst lengths of 1, 2,
4, or 8 locations are available for both the sequential
and the interleaved burst types, and a full-page burst is
available for the sequential type. The full-page burst is
used in conjunction with the BURST TERMINATE
command to generate arbitrary burst lengths.
Figure 5: Mode Register Definition
32,64 Meg x 64 SDRAM DIMMs
SD8_16C32_64x64AG_C.fm - Rev. C 11/02
8
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2002, Micron Technology Inc.
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