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DDR_x4x8x16_Core2.fm - 256Mb DDR: Rev. O, Core DDR: Rev. B 1/09 EN
59
2003 Micron Technology, Inc. All rights reserved.
256Mb: x4, x8, x16 DDR SDRAM
Operations
Figure 25:
Extended Mode Register Definition
Notes:
2. The reduced drive strength option is available only on Design Revision F and K.
3. The QFC# option is not supported.
ACTIVE
After a row is opened with an ACTIVE command, a READ or WRITE command may be
issued to that row, subject to the tRCD specification. tRCD (MIN) should be divided by
the clock period and rounded up to the next whole number to determine the earliest
clock edge after the ACTIVE command on which a READ or WRITE command can be
entered. For example, a tRCD specification of 20ns with a 133 MHz clock (7.5ns period)
any case where 2 < tRCD (MIN)/tCK ≤ 3 (Figure 26 also shows the same case for tRRD; the same procedure is used to convert other specification limits from time units to clock
cycles).
A row remains active (or open) for accesses until a PRECHARGE command is issued to
that bank. A PRECHARGE command must be issued before opening a different row in
the same bank.
A subsequent ACTIVE command to a different row in the same bank can only be issued
after the previous active row has been “closed” (precharged). The minimum time
interval between successive ACTIVE commands to the same bank is defined by tRC.
A subsequent ACTIVE command to another bank can be issued while the first bank is
being accessed, which results in a reduction of total row-access overhead. The minimum
time interval between successive ACTIVE commands to different banks is defined by
tRRD.
Operating Mode
Reserved
E3
0
–
E4
0
–
E1, E0
Valid
–
DLL
Enable
Disable
A9
A7 A6 A5 A4 A3
A8
A2 A1 A0
Extended mode
register (Ex)
Address bus
97
6
5
4
3
8
21
0
1
E0
0
1
Drive Strength
Normal
Reduced
E1
2
Operating Mode
. . .
An
BA1
BA0
. . .
n1
n + 1
n + 2
E6
0
–
E7
0
–
E8
0
–
E9
0
–
E5
0
–
. . .
0
–
En
0
–
DS
E2
3
0
–
Mn + 1
0
1
0
1
Mode Register Definition
Base mode register
Extended mode register
Reserved
Mn + 2
0
1
DLL
0
1
0