IS43R16800A1 datasheet(6/72 Pages) ISSI

6 / 72 page

Integrated Silicon Solution, Inc. — 1-800-379-4774

Rev. 00A

04/17/06

ISSI®

IS43R16800A1

Mode Register

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).

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.

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.

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.

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