HYB25D256[400/800/160]B[T/C](L)
256-Mbit Double Data Rate SDRAM
Functional Description
3.2.1
Burst Length
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.
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.
3.2.2
Burst Type
Accesses within a given burst may be programmed to be either sequential or interleaved; this is referred to as the
burst type and is selected via bit A3. The ordering of accesses within a burst is determined by the burst length, the
burst type and the starting column address, as shown in Table 5.
Table 5
Burst Definition
Burst
Starting Column Address
Order of Accesses Within a Burst
Length
A2
A1
A0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Type = Sequential
Type = Interleaved
0-1
2
4
0-1
1-0
1-0
0
0
1
1
0
0
1
1
0
0
1
1
0-1-2-3
0-1-2-3
1-2-3-0
1-0-3-2
2-3-0-1
2-3-0-1
3-0-1-2
3-2-1-0
8
0
0
0
0
1
1
1
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
Data Sheet
17
Rev. 1.21, 2004-07
02102004-TSR1-4ZWW
QIMONDA [ QIMONDA AG ]
