Rev. 1.0 / Mar. 2005

15

1

HY5DU12422C(L)TP

HY5DU12822C(L)TP

HY5DU121622C(L)TP

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 Definition Table

CAS LATENCY

The Read latency or CAS latency is the delay in clock cycles between the registration of a Read command and the

availability of the first burst of output data. The latency can be programmed 2 or 2.5 clocks for DDR200/266/333 and

3 clocks for DDR400. If a Read command is registered at clock edge n, and the latency is m clocks, the data is avail-

able nominally coincident with clock edge n + m.

Reserved states should not be used as unknown operation or incompatibility with future versions may result.

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