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WEDPN4M72V-XB2X Datasheet(PDF) 8 Page - White Electronic Designs Corporation |
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WEDPN4M72V-XB2X Datasheet(HTML) 8 Page - White Electronic Designs Corporation |
8 / 15 page 8 White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com White Electronic Designs WEDPN4M72V-XB2X January 2005 Rev. 2 White Electronic Designs Corp. reserves the right to change products or specifications without notice. ACTIVE The ACTIVE command is used to open (or activate) a row in a particular bank for a subsequent access. The value on the BA0, BA1 inputs selects the bank, and the address provided on inputs A0-11 selects the row. This row remains active (or open) for accesses until a PRECHARGE command is issued to that bank. A PRECHARGE command must be issued before opening a different row in the same bank. READ The READ command is used to initiate a burst read access to an active row. The value on the BA0, BA1 inputs selects the bank, and the address provided on inputs A0-7 selects 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 open for subsequent accesses. Read data appears on the I/Os subject to the logic level on the DQM inputs two clocks earlier. If a given DQM signal was registered HIGH, the corresponding I/Os will be High-Z two clocks later; if the DQM signal was registered LOW, the I/Os will provide valid data. WRITE The WRITE command is used to initiate a burst write access to an active row. The value on the BA0, BA1 inputs selects the bank, and the address provided on inputs A0-7 selects 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 open for subsequent accesses. Input data appearing on the I/Os is written to the memory array subject to the DQM input logic level appearing coincident with the data. If a given DQM signal is registered LOW, the corresponding data will be written to memory; if the DQM signal is registered HIGH, the corresponding data inputs will be ignored, and a WRITE will not be executed to that byte/column location. PRECHARGE The PRECHARGE command is used to deactivate the open row in a particular bank or the open row in all banks. The bank(s) will be available for a subsequent row access a specified time (tRP) after the PRECHARGE command is issued. Input A10 determines whether one or all banks are to be precharged, and in the case where only one bank is to be precharged, inputs BA0, BA1 select the bank. Otherwise BA0, BA1 are treated as “Don’t Care.” Once a bank has been precharged, it is in the idle state and must be activated prior to any READ or WRITE commands being issued to that bank. AUTO PRECHARGE AUTO PRECHARGE is a feature which performs the same individual-bank PRECHARGE function described above, without requiring an explicit command. This is accomplished by using A10 to enable AUTO PRECHARGE in conjunction with a specific READ or WRITE command. A precharge of the bank/row that is addressed with the READ or WRITE command is automatically performed upon completion of the READ or WRITE burst, except in the full-page burst mode, where AUTO PRECHARGE does not apply. AUTO PRECHARGE is nonpersistent in that it is either enabled or disabled for each individual READ or WRITE command. AUTO PRECHARGE ensures that the precharge is initiated at the earliest valid stage within a burst. The user must not issue another command to the same bank until the precharge time (tRP) is completed. This is determined as if an explicit PRECHARGE command was issued at the earliest possible time. BURST TERMINATE The BURST TERMINATE command is used to truncate either fixed-length or full-page bursts. The most recently registered READ or WRITE command prior to the BURST TERMINATE command will be truncated. AUTO REFRESH AUTO REFRESH is used during normal operation of the SDRAM and is analagous to CAS#-BEFORE-RAS# (CBR) REFRESH in conventional DRAMs. This command is nonpersistent, so it must be issued each time a refresh is required. The addressing is generated by the internal refresh controller. This makes the address bits “Don’t Care” during an AUTO REFRESH command. The 64Mb SDRAM requires 4,096 AUTO REFRESH cycles every refresh period (tREF), regardless of width option. Providing a distributed AUTO REFRESH command will meet the |
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