W332M72V-125SBI WEDC [White Electronic Designs Corporation], W332M72V-125SBI Datasheet - Page 4

• Manufacturer Part Number: W332M72V-125SBI
• Description: 32Mx72 Synchronous DRAM
• Manufacturer: WEDC [White Electronic Designs Corporation]

All inputs and outputs are LVTTL compatible. SDRAMs offer
sub stan tial ad vanc es in DRAM op er at ing per for mance,
in clud ing the ability to syn chro nous ly burst data at a high
data rate with au to mat ic column-ad dress gen er a tion,
the ability to in ter leave be tween in ter nal banks in order
to hide precharge time and the capability to ran dom ly
change col umn ad dress es on each clock cy cle dur ing a
burst ac cess.
FUNCTIONAL DE SCRIP TION
Read and write accesses to the SDRAM are burst oriented;
accesses start at a selected location and continue for a
pro grammed number of locations in a pro grammed
se quence. Ac cess es begin with the registration of an
ACTIVE com mand which is then followed by a READ or
WRITE com mand. The address bits registered coincident
with the AC TIVE 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) reg is tered
coincident with the READ or WRITE com mand are used to
select the start ing column location for the burst access.
Prior to normal operation, the SDRAM must be initialized.
The following sections provide detailed information
cov er ing device initialization, register defi nition, command
de scrip tions and de vice operation.
Initialization
SDRAMs must be pow ered up and initialized in a pre defi ned
manner. Operational pro ce dures other than those spec i fi ed
may result in undefi ned operation. Once power is ap plied
to V
(stable clock is de fi ned as a signal cycling within tim ing
constraints specified for the clock pin), the SDRAM
re quires 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 com mands should be applied.
Once the 100µs delay has been satisfi ed with at least
one COM MAND INHIBIT or NOP command having been
ap plied, 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
per formed. After the AUTO REFRESH cycles are complete,
the SDRAM is ready for Mode Register programming. Be cause
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
CC
and V
CCQ
(si mul ta neous ly) and the clock is stable
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4
Register Defi nition
MODE REGISTER
The Mode Register is used to defi ne the specifi c mode
of op er a tion of the SDRAM. This defi nition includes the
selec-tion of a burst length, a burst type, a CAS latency,
an op er at ing mode and a write burst mode, as shown in
Figure 3. The Mode Register is programmed via the LOAD
MODE REG IS TER command and will retain the stored
in for ma tion until it is programmed again or the device
loses power.
Mode register bits M0-M2 specify the burst length, M3
spec i fi es the type of burst (sequential or in ter leaved),
M4-M6 specify the CAS latency, M7 and M8 specify the
op er at ing mode, M9 spec i fi es the WRITE burst mode,
and M10 and M11 are reserved for future use. Address
A12 (M12) is undefi ned 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 specifi ed time before
ini ti at ing the subsequent operation. Violating either of these
requirements will result in unspecifi ed operation.
Burst Length
Read and write accesses to the SDRAM are burst oriented,
with the burst length being programmable, as shown in
Fig ure 3. The burst length determines the maximum
number of column lo ca tions that can be accessed for a
given READ or WRITE command. Burst lengths of 1, 2, 4
or 8 locations are avail able 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.
Reserved states should not be used, as unknown op er a tion
or incompatibility with future versions may result.
When a READ or WRITE command is issued, a block of
col umns equal to the burst length is effectively selected.
All accesses for that burst take place within this block,
mean ing 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 signifi cant)
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
White Electronic Designs Corporation • [phone] • www.wedc.com
W332M72V-XSBX