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W9725G6KB25A Datasheet(PDF) 20 Page - Winbond |
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W9725G6KB25A Datasheet(HTML) 20 Page - Winbond |
20 / 87 page W9725G6KB Publication Release Date: Sep. 03, 2012 - 20 - Revision A03 8.3 Command Function 8.3.1 Bank Activate Command ( CS = "L", RAS = "L", CAS = "H", WE = "H", BA0, BA1 = Bank, A0 to A12 be row address) The Bank Activate command must be applied before any Read or Write operation can be executed. Immediately after the bank active command, the DDR2 SDRAM can accept a read or write command on the following clock cycle. If a Read/Write command is issued to a bank that has not satisfied the tRCDmin specification, then additive latency must be programmed into the device to delay when the Read/Write command is internally issued to the device. The additive latency value must be chosen to assure tRCDmin is satisfied. Additive latencies of 0, 1, 2, 3, 4, 5 and 6 are supported. Once a bank has been activated it must be precharged before another Bank Activate command can be applied to the same bank. The bank active and precharge times are defined as tRAS and tRP, respectively. The minimum time interval between successive Bank Activate commands to the same bank is determined by the RAS cycle time of the device (tRC). The minimum time interval between Bank Activate commands is tRRD. T0 T1 T2 T3 Tn Tn+1 Tn+2 Tn+3 Bank A Row Addr. Bank A Col. Addr. Bank B Row Addr. Bank B Col. Addr. Bank A Addr. Bank B Addr. Bank A Row Addr. CAS - CAS delay time(tCCD) tRCD = 1 Additive Latency delay(AL) Read Begins Bank A Activate Bank A Post CAS Read Bank B Activate Bank B Post CAS Read Bank A Precharge Bank B Precharge Bank A Activate Bank Active ( ≥ tRAS) RAS Cycle time ( ≥ tRC) Bank Precharge time ( ≥ tRP) Command Address RAS - RAS delay time( ≥ tRRD) CLK CLK Internal RAS - RAS delay ( ≥ tRCDmin) Figure 12 – Bank activate command cycle: tRCD = 3, AL = 2, tRP = 3, tRRD = 2, tCCD = 2 8.3.2 Read Command ( CS = "L", RAS = "H", CAS = "L", WE = "H", BA0, BA1 = Bank, A10 = "L", A0 to A8 = Column Address) The READ command is used to initiate a burst read access to an active row. The value on BA0, BA1 inputs selects the bank, and the A0 to A8 address inputs determine the starting column address. The address 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 open for subsequent accesses. |
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