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AS4C64M16D2-25BIN Datasheet(PDF) 8 Page - Alliance Semiconductor Corporation |
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AS4C64M16D2-25BIN Datasheet(HTML) 8 Page - Alliance Semiconductor Corporation |
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8 / 58 page  AS4C64M16D2 Alliance Memory Inc. reserves the right to change products or specification without notice. 8 Rev. 1.1 April. /2012 Functional Description Read and write accesses to the DDR2 SDRAM are burst oriented; accesses start at a selected location and continue for a burst length of four or eight in a programmed sequence. Accesses begin with the registration of an Active command, which is then followed by a Read or Write command. The address bits registered coincident with the active command are used to select the bank and row to be accessed (BA0-BA2 select the bank; A0-A12 select the row). The address bits registered coincident with the Read or Write command are used to select the starting column location for the burst access and to determine if the auto precharge command is to be issued. Prior to normal operation, the DDR2 SDRAM must be initialized. The following sections provide detailed information covering device initialization, register definition, command descriptions, and device operation. • Power-up and Initialization DDR2 SDRAMs must be powered up and initialized in a predefined manner. Operational procedures other than those specified may result in undefined operation. The following sequence is required for POWER UP and Initialization. 1. Apply power and attempt to maintain CKE below 0.2*VDDQ and ODT *1 at a low state (all other inputs may be undefined.) The VDD voltage ramp time must be no greater than 200ms from when VDD ramps from 300mV to VDDmin; and during the VDD voltage ramp, |VDD-VDDQ| ≦ 0.3V - VDD, VDDL and VDDQ are driven from a single power converter output, AND - VTT is limited to 0.95 V max, AND - VREF tracks VDDQ/2. or - Apply VDD before or at the same time as VDDL. - Apply VDDL before or at the same time as VDDQ. - Apply VDDQ before or at the same time as VTT & VREF. At least one of these two sets of conditions must be met. 2. Start clock and maintain stable condition. 3. For the minimum of 200µs after stable power and clock (CK, CK#), then apply NOP or deselect and take CKE HIGH. 4. Wait minimum of 400ns then issue precharge all command. NOP or deselect applied during 400ns period. 5. Issue EMRS(2) command. (To issue EMRS (2) command, provide “LOW” to BA0 and BA2, “HIGH” to BA1.) 6. Issue EMRS (3) command. (To issue EMRS (3) command, provide “LOW” to BA2, “HIGH” to BA0 and BA1.) 7. Issue EMRS to enable DLL. (To issue "DLL Enable" command, provide "LOW" to A0, "HIGH" to BA0 and "LOW" to BA1 and BA2.) 8. Issue a Mode Register Set command for “DLL reset”. (To issue DLL reset command, provide "HIGH" to A8 and "LOW" to BA0-BA2) 9. Issue precharge all command. 10. Issue 2 or more auto-refresh commands. 11. Issue a mode register set command with LOW to A8 to initialize device operation. (i.e. to program operating parameters without resetting the DLL.) 12. At least 200 clocks after step 8, execute OCD Calibration (Off Chip Driver impedance adjustment).If OCD calibration is not used, EMRS OCD Default command (A9=A8=A7=HIGH) followed by EMRS OCD calibration Mode Exit command (A9=A8=A7=LOW) must be issued with other operating parameters of EMRS. 13. The DDR2 SDRAM is now ready for normal operation. NOTE 1: To guarantee ODT off, VREF must be valid and a LOW level must be applied to the ODT pin. |
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