Rev. 1.1 / May. 2005

18

BURST DEFINITION

BURST LENGTH & TYPE

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 com-

mand. 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.

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 Burst Definitionon Table

Burst Length

Starting Address (A2,A1,A0)

Sequential

Interleave

2

XX0

0, 1

0, 1

XX1

1, 0

1, 0

4

X00

0, 1, 2, 3

0, 1, 2, 3

X01

1, 2, 3, 0

1, 0, 3, 2

X10

2, 3, 0, 1

2, 3, 0, 1

X11

3, 0, 1, 2

3, 2, 1, 0

8

000

0, 1, 2, 3, 4, 5, 6, 7

0, 1, 2, 3, 4, 5, 6, 7

001

1, 2, 3, 4, 5, 6, 7, 0

1, 0, 3, 2, 5, 4, 7, 6

010

2, 3, 4, 5, 6, 7, 0, 1

2, 3, 0, 1, 6, 7, 4, 5

011

3, 4, 5, 6, 7, 0, 1, 2

3, 2, 1, 0, 7, 6, 5, 4

100

4, 5, 6, 7, 0, 1, 2, 3

4, 5, 6, 7, 0, 1, 2, 3

101

5, 6, 7, 0, 1, 2, 3, 4

5, 4, 7, 6, 1, 0, 3, 2

110

6, 7, 0, 1, 2, 3, 4, 5

6, 7, 4, 5, 2, 3, 0, 1

111

7, 0, 1, 2, 3, 4, 5, 6

7, 6, 5, 4, 3, 2, 1, 0