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Rev. A | July 2014

IS42/45SM/RM/VM16320E

Burst Length

Read and write accesses to the SDRAM are burst oriented, with the burst length being programmable, as shown in Figure 1. The burst

length determines the maximum number of column locations that can be accessed for a given READ or WRITE command. Burst

lengths of 1, 2, 4 or 8 locations are available for both the sequential and the interleaved burst types, and a full-page burst is available

for the sequential type. The full-page burst is used in conjunction with the BURST TERMINATE command to generate arbitrary burst

lengths.

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 will wrap within the block if a boundary is reached. The block is uniquely selected by A1-A9 when

the burst length is set to two; by A2-A9 when the burst length is set to four; and by A3-A9 when the burst length is set to eight. The

remaining (least significant) address bit(s) is (are) used to select the starting location within the block. Full-page bursts wrap within

the page if the boundary is reached.

Bank(Row) Active

The Bank Active command is used to activate a row in a specified bank of the device. This command is initiated by activating CS, RAS and

deasserting CAS, WE at the positive edge of the clock. The value on the BA0-BA1 selects the bank, and the value on the A0-A12 selects

the row.

This row remains active for column access until a precharge command is issued to that bank. Read and write operations can only be

initiated on this activated bank after the minimum tRCD time is passed from the activate command.

Read

The READ command is used to initiate the burst read of data. This command is initiated by activating CS, CAS, and deasserting WE, RAS at

the positive edge of the clock. BA0-BA1 input select the bank, A0-A9 address inputs select the starting column location. The value on input

A10 determines whether or not Auto Precharge is used. If Auto Precharge is selected the row being accessed will be precharged at the

end of the READ burst; if Auto Precharge is not selected, the row will remain active for subsequent accesses. The length of burst and the

CAS latency will be determined by the values programmed during the MRS command.

Write

The WRITE command is used to initiate the burst write of data. This command is initiated by activating CS, CAS, WE and deasserting RAS

at the positive edge of the clock. BA0-BA1 input select the bank, A0-A9 address inputs select the starting column location. The value on

input A10 determines whether or not Auto Precharge is used. If Auto Precharge is selected the row being accessed will be precharged at

the end of the WRITE burst; if Auto Precharge is not selected, the row will remain active for subsequent accesses.