256Mb: x4, x8, x16 DDR SDRAM
Operations
Table 27:
CAS Latency
Allowable Operating Clock Frequency (MHz)
Speed
-5B
-6/-6T
-75E
-75Z
-75
CL = 2
75
f
133
75
f
133
75
f
133
75
f
133
75
f
100
CL = 2.5
75
f
167
75
f
167
75
f
133
75
f
133
75
f
133
CL = 3
133
f
200
–
–
–
–
Operating Mode
The normal operating mode is selected by issuing an LMR command with bits A7–An
each set to zero and bits A[6:0] set to the desired values. A DLL reset is initiated by
issuing an LMR command with bits A7 and A[n:9] each set to zero, bit A8 set to one, and
bits A[6:0] set to the desired values. Although not required by the Micron device, JEDEC
specifications recommend that an LMR command resetting the DLL should always be
followed by an LMR command selecting normal operating mode.
All other combinations of values for A[n:7] are reserved for future use and/or test modes.
Test modes and reserved states should not be used, as unknown operation or incompat-
ibility with future versions may result.
Extended Mode Register
The extended mode register controls functions beyond those controlled by the mode
register; these additional functions are DLL enable/disable and output drive strength.
These functions are controlled via the bits shown in Figure 16 on page 59. The extended
mode register is programmed via the LMR command to the mode register (with BA0 = 1
and BA1 = 0) and will retain the stored information until it is programmed again or until
the device loses power. The enabling of the DLL should always be followed by an LMR
command to the mode register (BA0/BA1 = 0) to reset the DLL. The extended mode
register must be loaded when all banks are idle and no bursts are in progress, and the
controller must wait the specified time before initiating any subsequent operation.
Violating either requirement could result in an unspecified operation.
Output Drive Strength
The normal drive strength for all outputs is specified to be SSTL_2, Class II. The Design
Revision F and K devices support a programmable option for reduced drive. This option
is intended for the support of the lighter load and/or point-to-point environments. The
selection of the reduced drive strength will alter the DQ and DQS pins from SSTL_2,
Class II drive strength to a reduced drive strength, which is approximately 54% of the
SSTL_2, Class II drive strength.
DLL Enable/Disable
When the part is running without the DLL enabled, device functionality may be altered.
The DLL must be enabled for normal operation. DLL enable is required during power-
up initialization and upon returning to normal operation after having disabled the DLL
for the purpose of debug or evaluation (when the device exits self refresh mode, the DLL
is enabled automatically). Anytime the DLL is enabled, 200 clock cycles with CKE HIGH
must occur before a READ command can be issued.
PDF: 09005aef80768abb/Source: 09005aef82a95a3a
DDR_x4x8x16_Core2.fm - 256Mb DDR: Rev. S, Core DDR: Rev. E 9/12 EN
58
Micron Technology, Inc., reserves the right to change products or specifications without notice.
©2003 Micron Technology, Inc. All rights reserved.
MICRON [ MICRON TECHNOLOGY ]
