i PEM
2.4 Gb SDRAM-DDR2
Gb
Austin Semiconductor, Inc.
AS4DDR232M72PBG
TABLE 2 - BURST DEFINITION
Burst
Length
Starting Column
Address
A1
0
4
0
1
1
A2
0
0
0
8
0
1
1
1
1
A1
0
0
1
1
0
0
1
1
A0
0
1
0
1
A0
0
1
0
1
0
1
0
1
0-1-2-3-4-5-6-7
1-2-3-4-5-6-7-0
2-3-4-5-6-7-0-1
3-4-5-6-7-0-1-2
4-5-6-7-0-1-2-3
5-6-7-0-1-2-3-4
6-7-0-1-2-3-4-5
7-0-1-2-3-4-5-6
0-1-2-3-4-5-6-7
1-0-3-2-5-4-7-6
2-3-0-1-6-7-4-5
3-2-1-0-7-6-5-4
4-5-6-7-0-1-2-3
5-4-7-6-1-0-3-2
6-7-4-5-2-3-0-1
7-6-5-4-3-2-1-0
0-1-2-3
1-2-3-0
2-3-0-1
3-0-1-2
0-1-2-3
1-0-3-2
2-3-0-1
3-2-1-0
Order of Accesses Within a Burst
Type = Sequential
Type = Interleaved
DLL RESET
DLL RESET is defined by bit M8, as shown in Figure 5.
Programming bit M8 to “1” will activate the DLL RESET
function. Bit M8 is self-clearing, meaning it returns back
to a value of ¡°0¡± after the DLL RESET function has been
issued.
Anytime the DLL RESET function is used, 200 clock cycles
must occur before a READ command can be issued to allow
time for the internal clock to be synchronized with the external
clock. Failing to wait for synchronization to occur may result
in a violation of the
t
AC or
t
DQSCK parameters.
WRITE RECOVERY
Write recovery (WR) time is defined by bits M9-M11, as shown
in Figure 5. The WR register is used by the DDR2 SDRAM
during WRITE with auto precharge operation. During WRITE
with auto precharge operation, the DDR2 SDRAM delays
the internal auto precharge operation by WR clocks
(programmed in bits M9-M11) from the last data burst.
WR values of 2, 3, 4, 5, or 6 clocks may be used for
programming bits M9-M11. The user is required to program
the value of WR, which is calculated by dividing
t
WR (in ns)
by
t
CK (in ns) and rounding up a non integer value to the next
integer; WR [cycles] =
t
WR [ns] /
t
CK [ns]. Reserved states
should not be used as unknown operation or incompatibility
with future versions may result.
NOTES:
1. For a burst length of two, A1-Ai select two-data-element block;
A0 selects the starting column within the block.
2. For a burst length of four, A2-Ai select four-data-element block;
A0-1 select the starting column within the block.
3. For a burst length of eight, A3-Ai select eight-data-element block;
A0-2 select the starting column within the block.
4. Whenever a boundary of the block is reached within a given
sequence above, the following access wraps within the block.
OPERATING MODE
The normal operating mode is selected by issuing a
command with bit M7 set to ¡°0,¡± and all other bits set to
the desired values, as shown in Figure 5. When bit M7 is
“1,” no other bits of the mode register are programmed.
Programming bit M7 to ¡°1¡± places the DDR2 SDRAM into a
test mode that is only used by the manufacturer and should
not be used. No operation or functionality is guaranteed
if M7 bit is “1.”
POWER-DOWN MODE
Active power-down (PD) mode is defined by bit M12, as
shown in Figure 5. PD mode allows the user to determine
the active power-down mode, which determines
performance versus power savings. PD mode bit M12 does
not apply to precharge PD mode.
When bit M12 = 0, standard active PD mode or “fast-exit”
active PD mode is enabled. The
t
XARD parameter is used
for fast-exit active PD exit timing. The DLL is expected to be
enabled and running during this mode.
When bit M12 = 1, a lower-power active PD mode or “slowexit”
active PD mode is enabled. The
t
XARD parameter is used
for slow-exit active PD exit timing. The DLL can be enabled,
but “frozen” during active PD mode since the exit-to-READ
command timing is relaxed. The power difference expected
between PD normal and PD low-power mode is defined in
the I
CC
table.
AS4DDR232M72PBG
Rev. 2.0 5/07
Austin Semiconductor, Inc.
●
Austin, Texas
●
512.339.1188
●
www.austinsemiconductor.com
9
AUSTIN [ AUSTIN SEMICONDUCTOR ]
