SDRAM
AS4SD8M16
Austin Semiconductor, Inc.
FUNCTIONAL DESCRIPTION
operation of the SDRAM. This definition includes the
selection of a burst length, a burst type, a CAS latency, an op-
erating mode and a write burst mode, as shown in Figure 1.
The mode register is programmed 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 interleaved), 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.
In general, the 128Mb SDRAMs are quad-bank DRAMs
that operate at 3.3V and include a synchronous interface (all
signals are registered on the positive edge of the clock signal,
CLK). Each of the 33,554,432-bit banks is organized as 4,096
rows by 512 columns by 16 bits.
Read and write accesses to the SDRAM are burst oriented;
accesses start at a selected location and continue for a
programmed number of locations in a programmed sequence.
Accesses begin with the registration of anACTIVE command,
which is then followed by a READ or WRITE command. The
address bits registered coincident with the ACTIVE command
are used to select the bank and row to be accessed (BA0 and
BA1 select the bank, A0 - A11 select the row). The address
bits (A0 -A8) registered coincident with the READ or WRITE
command are used to select the starting column location for
the burst access.
The mode register must be loaded when all banks are idle,
and the controller must wait the specified time before initiat-
ing the subsequent operation. Violating either of these
requirements will result in unspecified operation.
Burst Length
Prior to normal operation, the SDRAM must be initial-
ized. The following sections provide detailed information cov-
ering device initialization, register definition, command de-
scriptions and device operation.
Read and write accesses to the SDRAM are burst oriented,
with the burst length being programmable, as shown in Figure
1. The burst length determines the maximum number of col-
umn 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 types. The
full-page burst is used in conjunction with the BURST
TERMINATE command to generate arbitrary burst lengths.
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. The clock is uniquely selected by A1-A8 when the
burst length is set to two; by A2-A8 when the burst length is
set to four, and by A3-A8 when the burst length is set to eight.
The remaining (least significant) address bit(s) is (are) used to
Initialization
SDRAMs must be powered up and initialized in a pre-
defined manner. Operational procedures other than those speci-
fied may result in undefined operation. Once power is applied
to VDD and VDDQ (simultaneously) and the clock is stable
(stable clock is defined as a signal cycling within timing con-
straints specified for the clock pin), the SDRAM requires a
100µs delay prior to issuing any command other than a COM-
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 commands 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 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 preformed. After the AUTO REFRESH cycles are com-
plete, 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.
select
the
starting location within the block. Full-page bursts wrap within
the page if the boundary is reached.
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 accesses within a burst is determined by
the burst length, the burst type and the starting column
address, shown in table 1.
Register Definition
MODE REGISTER
The mode register is used to define the specific mode of
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
AS4SD8M16
Rev. 0.5 04/05
4
AUSTIN [ AUSTIN SEMICONDUCTOR ]
