A48P3616A
Register Definition
Mode Register
Burst Length
The Mode Register is used to define the specific mode of
operation of the DDR SDRAM. This definition includes the
selection of a burst length, a burst type, a CAS latency, and
an operating mode. The Mode Register is programmed via
the Mode Register Set command (with BA0 = 0 and BA1 = 0)
and retains the stored information until it is programmed
again or the device loses power (except for bit A8, which is
self-clearing).
Read and write accesses to the DDR SDRAM are burst
oriented, with the burst length being programmable. The
burst length determines the maximum number of column
locations that can be accessed for a given Read or Write
command. Burst lengths of 2, 4, or 8 locations are available
for both the sequential and the interleaved burst types.
Reserved states should not be used, as unknown operation
or incompatibility with future versions may result.
Mode Register bits A0-A2 specify the burst length, A3
specifies the type of burst (sequential or interleaved), A4-A6
specify the CAS latency, and A7-A11 specify the operating
mode.
When a Read or Write command is issued, a block of
columns equal to the burst length is effectively selected. All
accesses for that burst take place within this block, meaning
that the burst wraps within the block if a boundary is reached.
The block is uniquely selected by A1-Ai when the burst
length is set to two, by A2-Ai when the burst length is set to
four and by A3-Ai when the burst length is set to eight (where
Ai is the most significant column address bit for a given
configuration). The remaining (least significant) address bit(s)
is (are) used to select the starting location within the block.
The programmed burst length applies to both Read and
Write bursts.
The Mode Register must be loaded when all banks are idle,
and the controller must wait the specified time before
initiating the subsequent operation. Violating either of these
requirements results in unspecified operation.
Mode Register Operation
BA0
0*
A11
A10
A9
A8
A7
A6
A5
A4
A3
BT
A2
A1
A0
Address Bus
BA1
0*
Operating Mode
CAS Latency
Burst Length
Mode Register
CAS Latency
A3 Burst Type
Burst Length
Operating Mode
A11-A9 A8 A7 A6-A0
Type
A6
A5
A4
Type
0
1
Sequential A2 A1 A0
Type
Normal operation
Do not reset DLL
0
0
0
1
0
0
Valid
Valid
0
0
0
Reserved
Interleave
0
0
0
0
0
1
Reserved
Normal operation
in DLL Reset
0
0
1
Reserved
2
0
0
1
1
1
1
1
1
0
0
1
1
0
1
0
1
0
1
2
0
0
1
1
1
1
1
1
0
0
1
1
0
1
0
1
0
1
4
3
4
8
Reserved
Reserved
Reserved
Reserved
Reserved
2.5
Reserved
Note:
* BA0 and BA1 must be 0, 0 to select the Mode Register
(vs. the Extended Mode Register).
PRELIMINARY (July, 2010, Version 0.0)
6
AMIC Technology, Corp.
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