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GS81302T18E-333I 데이터시트(PDF) 8 Page - GSI Technology |
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GS81302T18E-333I 데이터시트(HTML) 8 Page - GSI Technology |
8 / 36 page GS81302T08/09/18/36E-375/350/333/300/250 Specifications cited are subject to change without notice. For latest documentation see http://www.gsitechnology.com. Rev: 1.03b 12/2011 8/35 © 2011, GSI Technology Special Functions Byte Write and Nybble Write Control Byte Write Enable pins are sampled at the same time that Data In is sampled. A high on the Byte Write Enable pin associated with a particular byte (e.g., BW0 controls D0–D8 inputs) will inhibit the storage of that particular byte, leaving whatever data may be stored at the current address at that byte location undisturbed. Any or all of the Byte Write Enable pins may be driven high or low during the data in sample times in a write sequence. Each write enable command and write address loaded into the RAM provides the base address for a 2 beat data transfer. The x18 version of the RAM, for example, may write 36 bits in association with each address loaded. Any 9-bit byte may be masked in any write sequence. Nybble Write (4-bit) write control is implemented on the 8-bit-wide version of the device. For the x8 version of the device, “Nybble Write Enable” and “NBx” may be substituted in all the discussion above. Example x18 RAM Write Sequence using Byte Write Enables Data In Sample Time BW0 BW1 D0–D8 D9–D17 Beat 1 0 1 Data In Don’t Care Beat 2 1 0 Don’t Care Data In Resulting Write Operation Byte 1 D0–D8 Byte 2 D9–D17 Byte 3 D0–D8 Byte 4 D9–D17 Written Unchanged Unchanged Written Beat 1 Beat 2 Output Register Control SigmaDDR-II SRAMs offer two mechanisms for controlling the output data registers. Typically, control is handled by the Output Register Clock inputs, C and C. The Output Register Clock inputs can be used to make small phase adjustments in the firing of the output registers by allowing the user to delay driving data out as much as a few nanoseconds beyond the next rising edges of the K and K clocks. If the C and C clock inputs isare tied high, the RAM reverts to K and K control of the outputs, allowing the RAM to function as a conventional pipelined read SRAM. FLXDrive-II Output Driver Impedance Control HSTL I/O SigmaDDR-II SRAMs are supplied with programmable impedance output drivers. The ZQ pin must be connected to VSS via an external resistor, RQ, to allow the SRAM to monitor and adjust its output driver impedance. The value of RQ must be 5X the value of the desired RAM output impedance at mid-rail. The allowable range of RQ to guarantee impedance matching continuously is between 175 Ω and 350Ω. Periodic readjustment of the output driver impedance is necessary as the impedance is affected by drifts in supply voltage and temperature. The SRAM’s output impedance circuitry compensates for drifts in supply voltage and temperature. A clock cycle counter periodically triggers an impedance evaluation, resets and counts again. Each impedance evaluation may move the output driver impedance level one step at a time towards the optimum level. The output driver is implemented with discrete binary weighted impedance steps. |
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