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AS4LC8M8S0 Datasheet(PDF) 11 Page - Alliance Semiconductor Corporation |
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AS4LC8M8S0 Datasheet(HTML) 11 Page - Alliance Semiconductor Corporation |
11 / 24 page ® AS4LC8M8S0 AS4LC4M16S0 7/5/00 ALLIANCE SEMICONDUCTOR 11 Device operation (continued) Command Pin Settings Description Burst stop CS = WE = low; RAS = CAS = high Use burst stop to terminate burst operation. This command may be used to terminate all legal burst lengths. Bank precharge CS = A10 = RAS = WE = low; CAS = high; A11 = bank select; A0~A9 = don’t care The Bank Precharge command precharges the bank specified by BA0 and BA1. The precharged bank is switched from active to idle state and is ready to be activated again. Assert the precharge command after tRAS(min) of the bank activate command in the specified bank. The precharge operation requires a time of tRP(min) to complete. Precharge all CS = RAS = WE = low; CAS = A10 = high; BA0~BA1 = bank select; A0~A9 = don’t care The Precharge All command precharges all four banks simultaneously. All four banks are switched to the idle state on precharge completion. Auto precharge CS = CAS = WE (write) = low; RAS = WE (read) = A10 = high; BA0~BA1 = bank select; A0~A9 = column address; (A9 = don’t care for 2M ×8; A8,A9 = don’t care for 1M ×16) During auto precharge, the SDRAM adjusts internal timing to satisfy tRAS(min) and tRP for the programmed CAS latency and burst length. Couple the auto precharge with a burst read/write operation by asserting A10 to a high state at the same time the burst read/write commands are issued. At auto precharge completion, the specified bank is switched from active to idle state. Note that no new commands to the bank can be issued until the specified bank achieves the idle state. Auto precharge doesn’t work with full-page burst. Clock suspend/power down mode entry CKE = low When CKE is low, the internal clock is frozen or suspended from the next clock cycle and the state of the output and burst address are frozen. If all banks are idle and CKE goes low, the SDRAM enters power down mode at the next clock cycle. When in power down mode, no input commands are acknowledged as long as CKE remains low. To exit power down mode, raise CKE high before the rising edge of CLK. Clock suspend/power down mode exit CKE = high Resume internal clock operation by asserting CKE high before the rising edge of CLK. Subsequent commands can be issued one clock cycle after the end of the Exit command. Auto refresh CS = RAS = CAS = low; WE = CKE = high; A0~A11 = don’t care SDRAM storage cells must be refreshed every 64ms to maintain data integrity. Use the Auto Refresh command to refresh all rows in all banks of the SDRAM. The row address is provided by an internal counter which increments automatically. Auto refresh can only be asserted when all four banks are idle and the device is not in the power down mode. The time required to complete the auto refresh operation is tRC(min). Use NOPs in the interim until the auto refresh operation is complete. This is the most common refresh mode. It is typically performed once every 15.6us or in a burst of 4096 auto refresh cycles every 64ms. All four banks will be in the idle state after this operation. Self refresh CS = RAS = CAS = CKE = low; WE = high; A0~A11 = don’t care Self refresh is another mode for refreshing SDRAM cells. In this mode, refresh address and timing are provided internally. Self refresh entry is allowed only when all four banks are idle. The internal clock and all input buffers with the exception of CKE are disabled in this mode. Exit self refresh by restarting the external clock and then asserting CKE high. NOP’s must follow for a time of tRC(min) for the SDRAM to reach the idle state where normal operation is allowed. If burst auto refresh is used in normal operation, burst 4096 auto refresh cycles immediately after exiting self refresh. |
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