W332M72V-XSBX
White Electronic Designs
All inputs and outputs are LVTTLcompatible. SDRAMs offer
Register Definition
substantial advances in DRAM operating performance,
including the ability to synchronously burst data at a high
data rate with automatic column-address generation,
the ability to interleave between internal banks in order
to hide precharge time and the capability to randomly
change column addresses on each clock cycle during a
burst access.
MODE REGISTER
The Mode Register is used to define the specific mode
of operation of the SDRAM. This definition includes the
selec-tion of a burst length, a burst type, a CAS latency,
an operating mode and a write burst mode, as shown in
Figure 3. 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.
FUNCTIONAL DESCRIPTION
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 an
ACTIVE 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,
A0-12 select the row). The address bits (A0-9) registered
coincident with the READ or WRITE command are used to
select the starting column location for the burst access.
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. 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.
Prior to normal operation, the SDRAM must be initialized.
The following sections provide detailed information
covering device initialization, register definition, command
descriptions and device operation.
Burst Length
Read and write accesses to the SDRAM are burst oriented,
with the burst length being programmable, as shown in
Figure 3. 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
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.
Initialization
SDRAMs must be powered up and initialized in a predefined
manner. Operational procedures other than those specified
may result in undefined operation. Once power is applied
to VCC and VCCQ (simultaneously) and the clock is stable
(stable clock is defined as a signal cycling within timing
constraints specified for the clock pin), the SDRAM
requires a 100µs delay prior to issuing any command
other than a COMMAND INHIBIT or a 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.
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 block is uniquely selected by
A1-9 when the burst length is set to two; by A2-9 when
the burst length is set to four; and by A3-9 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
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 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,
theSDRAMisreadyforModeRegisterprogramming. Because
the Mode Register will power up in an unknown state, it should
be loaded prior to applying any operational command.
Ju;y 2006
Rev. 3
4
White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com
WEDC [ WHITE ELECTRONIC DESIGNS CORPORATION ]
