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IS46LR32200B Datasheet(PDF) 11 Page - Integrated Silicon Solution, Inc |
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IS46LR32200B Datasheet(HTML) 11 Page - Integrated Silicon Solution, Inc |
11 / 42 page 11 Rev. A | Feb. 2013 www.issi.com - dram@issi.com IS43/46LR32200B Mode Register The mode register is used to define the specific mode of operation of the Mobile DDR SDRAM. This definition includes the selection of a burst length, a burst type, a CAS latency. The mode register is programmed via the LOAD MODE REGISTER command and will retain the stored information until programmed again, the device goes into deep power-down mode, or the device loses power. 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-A10 should be set to zero. BA0 and BA1 must be zero to access the mode register. 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 will result in unspecified operation. Burst Length Read and write accesses to the Mobile DDR SDRAM are burst oriented, with the burst length being programmable, as shown in Figure (Mode Register Set Definition). 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, 4,8 or 16 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 will wrap within the block if a boundary is reached. The block is uniquely selected by A1-A7 when the burst length is set to two; by A2-A7 when the burst length is set to four; by A3-A7 when the burst length is set to eight; and by A4-A7 when the burst length is set to sixteen. 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. CAS Latency The CAS latency is the delay, in clock cycles, between the registration of a READ command and the availability of the first bit of output data. The latency can be set to 2, 3 clocks, as shown in Figure (Standard Mode Register Definition). For CL = 3, if the READ command is registered at clock edge n, then the data will be available at (n + 2 clocks + tAC). For CL = 2, if the READ command is registered at clock edge n, then the data will be available at (n + 1 clock + tAC). Figure7 : CAS Latency (BL=4) /C K C K Command T0 T1 T2 T3 T1n T2n T3n READ NOP NOP NOP DQS DQ tAC CL=3 DOUT n+1 tRPRE 2tCK T4 T4n NOP tRPST DOUT n DOUT n+2 DOUT n+3 Don ’t care DQS DQ tAC CL=2 D OUT n+1 tRPRE 1tCK tRPST DOUT n DOUT n+2 DOUT n+3 L L |
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