White Electronic Designs
TRUTH TABLE - COMMANDS (NOTE 1)
NAME (FUNCTION)
DESELECT (NOP) (9)
NO OPERATION (NOP) (9)
ACTIVE (Select bank and activate row) ( 3)
READ (Select bank and column, and start READ burst) (4)
WRITE (Select bank and column, and start WRITE burst) (4)
BURST TERMINATE (8)
PRECHARGE (Deactivate row in bank or banks) ( 5)
AUTO REFRESH or SELF REFRESH (Enter self refresh mode) (6, 7)
LOAD MODE REGISTER (2)
CS#
H
L
L
L
L
L
L
L
L
RAS#
X
H
L
H
H
H
L
L
L
W3E32M72S-XSBX
CAS#
X
H
H
L
L
H
H
L
L
WE#
X
H
H
H
L
L
L
H
L
ADDR
X
X
Bank/Row
Bank/Col
Bank/Col
X
Code
X
Op-Code
TRUTH TABLE - DM OPERATION
NAME (FUNCTION)
WRITE ENABLE (10)
WRITE INHIBIT (10)
NOTES:
1. CKE is HIGH for all commands shown except SELF REFRESH.
2. A0-12 define the op-code to be written to the selected Mode Register. BA0, BA1
select either the mode register (0, 0) or the extended mode register (1, 0).
3. A0-12 provide row address, and BA0, BA1 provide bank address.
4. A0-9 provide column address; A10 HIGH enables the auto precharge feature (non
persistent), while A10 LOW disables the auto precharge feature; BA0, BA1 provide
bank address.
5. A10 LOW: BA0, BA1 determine the bank being precharged. A10 HIGH: All banks
precharged and BA0, BA1 are “Don’t Care.”
DM
L
H
6.
DQs
Valid
X
This command is AUTO REFRESH if CKE is HIGH; SELF REFRESH if CKE is
LOW.
7. Internal refresh counter controls row addressing; all inputs and I/Os are “Don’t
Care” except for CKE.
8. Applies only to read bursts with auto precharge disabled; this command is
undefined (and should not be used) for READ bursts with auto precharge enabled
and for WRITE bursts.
9. DESELECT and NOP are functionally interchangeable.
10. Used to mask write data; provided coincident with the corresponding data.
during an AUTO REFRESH command. Each DDR SDRAM
requires AUTO REFRESH cycles at an average interval
of 7.8125µs (maximum).
To allow for improved efficiency in scheduling and
switching between tasks, some flexibility in the absolute
refresh interval is provided. A maximum of eight AUTO
REFRESH commands can be posted to any given DDR
SDRAM, meaning that the maximum absolute interval
between any AUTO REFRESH command and the next
AUTO REFRESH command is 9 x 7.8125µs (70.3µs). This
maximum absolute interval is to allow future support for
DLL updates internal to the DDR SDRAM to be restricted
to AUTO REFRESH cycles, without allowing excessive
drift in t
AC
between updates.
Although not a JEDEC requirement, to provide for future
functionality features, CKE must be active (High) during
the AUTO REFRESH period. The AUTO REFRESH period
begins when the AUTO REFRESH command is registered
and ends t
RFC
later.
SELF REFRESH*
The SELF REFRESH command can be used to retain
data in the DDR SDRAM, even if the rest of the system is
powered down. When in the self refresh mode, the DDR
SDRAM retains data without external clocking. The SELF
REFRESH command is initiated like an AUTO REFRESH
command except CKE is disabled (LOW). The DLL is
automatically disabled upon entering SELF REFRESH and
is automatically enabled upon exiting SELF REFRESH (A
DLL reset and 200 clock cycles must then occur before a
READ command can be issued). Input signals except CKE
are “Don’t Care” during SELF REFRESH. VREF voltage is
also required for the full duration of SELF REFRESH.
The procedure for exiting self refresh requires a sequence
of commands. First, CK and CK# must be stable prior
to CKE going back HIGH. Once CKE is HIGH, the DDR
SDRAM must have NOP commands issued for t
XSNR
,
because time is required for the completion of any internal
refresh in progress.
White Electronic Designs Corp. reserves the right to change products or specifications without notice.
July 2006
Rev. 6
9
White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com
WEDC [ WHITE ELECTRONIC DESIGNS CORPORATION ]
