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MT48LC4M32B2 Datasheet(PDF) 11 Page - Micron Technology |
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MT48LC4M32B2 Datasheet(HTML) 11 Page - Micron Technology |
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11 / 52 page  11 128Mb: x32 SDRAM Micron Technology, Inc., reserves the right to change products or specifications without notice. 128MbSDRAMx32_D.p65 – Rev. D; Pub. 6/02 ©2002, Micron Technology, Inc. 128Mb: x32 SDRAM COMMAND INHIBIT The COMMAND INHIBIT function prevents new commands from being executed by the SDRAM, re- gardless of whether the CLK signal is enabled. The SDRAM is effectively deselected. Operations already in progress are not affected. NO OPERATION (NOP) The NO OPERATION (NOP) command is used to perform a NOP to an SDRAM which is selected (CS# is LOW). This prevents unwanted commands from being registered during idle or wait states. Operations already in progress are not affected. LOAD MODE REGISTER The mode register is loaded via inputs A0-A11. See mode register heading in the Register Definition sec- tion. The LOAD MODE REGISTER command can only be issued when all banks are idle, and a subsequent executable command cannot be issued until tMRD is met. 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 and BA1 inputs selects the bank, and the address provided on inputs A0–A11 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 open- ing 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 and BA1 (B1) inputs selects the bank, and the address provided on inputs A0–A7 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 DQs subject to the logic level on the DQM inputs two clocks earlier. If a given DQMx signal was registered HIGH, the corresponding DQs will be High-Z two clocks later; if the DQMx signal was regis- tered LOW, the corresponding DQs will provide valid data. DQM0 corresponds to DQ0–DQ7, DQM1 corre- sponds to DQ8–DQ15, DQM2 corresponds to DQ16– DQ23 and DQM3 corresponds to DQ24–DQ31. WRITE The WRITE command is used to initiate a burst write access to an active row. The value on the BA0 and BA1 inputs selects the bank, and the address provided on inputs A0-A7 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 DQs is written to the memory array subject to the DQM input logic level appearing coinci- dent 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 correspond- ing 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 and BA1 select the bank. Otherwise BA0 and 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 de- scribed 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 ad- dressed with the READ or WRITE command is auto- matically 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 non- persistent in that it is either enabled or disabled for each individual READ or WRITE command. Auto precharge ensures that the precharge is initi- ated 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, as described for each burst type in the Operation section of this data sheet. |
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