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W3E16M64S-200BI Datasheet(PDF) 4 Page - White Electronic Designs Corporation |
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W3E16M64S-200BI Datasheet(HTML) 4 Page - White Electronic Designs Corporation |
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4 / 16 page  4 White Electronic Designs Corporation • (602) 437-1520 • www.wedc.com White Electronic Designs W3E16M64S-XBX February 2005 Rev. 4 Prior to normal operation, the SDRAM must be initialized. The following sections provide detailed information covering device initialization, register definition, command descriptions and device operation. INITIALIZATION DDR SDRAMs must be powered up and initialized in a predefined manner. Operational procedures other than those specified may result in undefined operation. Power must first be applied to VCC and VCCQ simultaneously, and then to VREF (and to the system VTT). VTT must be applied after VCCQ to avoid device latch-up, which may cause permanent damage to the device. VREF can be applied any time after VCCQ but is expected to be nominally coincident with VTT. Except for CKE, inputs are not recognized as valid until after VREF is applied. CKE is an SSTL_2 input but will detect an LVCMOS LOW level after VCC is applied. Maintaining an LVCMOS LOW level on CKE during power- up is required to ensure that the DQ and DQS outputs will be in the High-Z state, where they will remain until driven in normal operation (by a read access). After all power supply and reference voltages are stable, and the clock is stable, the DDR SDRAM requires a 200 ∝s delay prior to applying an executable command. Once the 200 ∝s delay has been satisfied, a DESELECT or NOP command should be applied, and CKE should be brought HIGH. Following the NOP command, a PRECHARGE ALL command should be applied. Next a LOAD MODE REGISTER command should be issued for the extended mode register (BA1 LOW and BA0 HIGH) to enable the DLL, followed by another LOAD MODE REGISTER command to the mode register (BA0/BA1 both LOW) to reset the DLL and to program the operating parameters. Two-hundred clock cycles are required between the DLL reset and any READ command. A PRECHARGE ALL command should then be applied, placing the device in the all banks idle state. Once in the idle state, two AUTO REFRESH cycles must be performed (tRFC must be satisfied.) Additionally, a LOAD MODE REGISTER command for the mode register with the reset DLL bit deactivated (i.e., to program operating parameters without resetting the DLL) is required. Following these requirements, the DDR SDRAM is ready for normal operation. and by the memory contoller during WRITEs. DQS is edge- aligned with data for READs and center-aligned with data for WRITEs. Each chip has two data strobes, one for the lower byte and one for the upper byte. The 128MB DDR SDRAM operates from a differential clock (CLK and CLK#); the crossing of CLK going HIGH and CLK# going LOW will be referred to as the positive edge of CLK. Commands (address and control signals) are registered at every positive edge of CLK. Input data is registered on both edges of DQS, and output data is referenced to both edges of DQS, as well as to both edges of CLK. Read and write accesses to the DDR SDRAM are burst oriented; accesses start at a selected location and continue for a programmed number of locations 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. The address bits registered coincident with the READ or WRITE command are used to select the bank and the starting column location for the burst access. The DDR SDRAM provides for programmable READ or WRITE burst lengths of 2, 4, or 8 locations. An auto precharge function may be enabled to provide a self- timed row precharge that is initiated at the end of the burst access. The pipelined, multibank architecture of DDR SDRAMs allows for concurrent operation, thereby providing high effective bandwidth by hiding row precharge and activation time. An auto refresh mode is provided, along with a power- saving power-down mode. FUNCTIONAL DESCRIPTION Read and write accesses to the DDR SDRAM are burst oriented; accesses start at a selected location and continue for a programmed number of locations 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 and BA1 select the bank, A0-12 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. |
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