1HY5DU573222F(P)
Rev. 1.0 / Feb. 2005 18
BURST DEFINITION
BURST LENGTH & TYPE
Read and write accesses to th e DDR SD RAM are bu rst orien ted, wi th 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 se t 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 f or a
given configuration). The remaining (least significant) address bit(s) is (are) used to select the starting location withi n
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
2XX0 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