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W3E232M16S-200STI Datasheet(PDF) 5 Page - White Electronic Designs Corporation |
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W3E232M16S-200STI Datasheet(HTML) 5 Page - White Electronic Designs Corporation |
5 / 22 page W3E232M16S-XSTX 5 White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com White Electronic Designs December 2005 Rev. 1 White Electronic Designs Corp. reserves the right to change products or specifications without notice. PRELIMINARY* BURST LENGTH Read and write accesses to the DDR SDRAM are burst oriented, with the burst length being programmable, as shown in Figure 3. 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 will wrap 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 (where Ai is the most significant column address for a given configuration); and by A3-Ai 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. The programmed burst length applies to both READ and WRITE bursts. BURST TYPE 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 M3. The ordering of accesses within a burst is determined by the burst length, the burst type and the starting column address, as shown in Table 1. READ LATENCY The READ 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 or 2.5 clocks. If a READ command is registered at clock edge n, and the latency is m clocks, the data will be available by clock edge n+m. Table 2 below indicates the operating frequencies at which each CAS latency setting can be used. Reserved states should not be used as unknown operation or incompatibility with future versions may result. be brought HIGH. Following the NOP command, a PRECHARGE ALL command should be applied. Next a LOAD MODE REGISTER command should be issued for the extended mode register (BA1 LOW and BA0 HIGH) to enable the DLL, followed by another LOAD MODE REGISTER command to the mode register (BA0/BA1 both LOW) to reset the DLL and to program the operating parameters. Two-hundred clock cycles are required between the DLL reset and any READ command. A PRECHARGE ALL command should then be applied, placing the device in the all banks idle state. Once in the idle state, two AUTO REFRESH cycles must be performed (tRFC must be satisfied.) Additionally, a LOAD MODE REGISTER command for the mode register with the reset DLL bit deactivated (i.e., to program operating parameters without resetting the DLL) is required. Following these requirements, the DDR SDRAM is ready for normal operation. REGISTER DEFINITION 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, as shown in Figure 3. The Mode Register is programmed via the MODE REGISTER SET command (with BA0 = 0 and BA1 = 0) and will retain the stored information until it is programmed again or the device loses power. (Except for bit A8 which is self clearing). Reprogramming the mode register will not alter the contents of the memory, provided it is performed correctly. The Mode Register must be loaded (reloaded) when all banks are idle and no bursts are in progress, and the controller must wait the specified time before initiating the subsequent operation. Violating either of these requirements will result in unspecified operation. 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-A12 specify the operating mode. |
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