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W9751G6KB-25 Datasheet(PDF) 16 Page - Winbond |
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W9751G6KB-25 Datasheet(HTML) 16 Page - Winbond |
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16 / 87 page  W9751G6KB Publication Release Date: Sep. 03, 2012 - 16 - Revision A04 8.2.3.1 Extended Mode Register for OCD Impedance Adjustment OCD impedance adjustment can be done using the following EMRS mode. In drive mode all outputs are driven out by DDR2 SDRAM. In Drive (1) mode, all DQ, DQS signals are driven HIGH and all DQS signals are driven LOW. In Drive (0) mode, all DQ, DQS signals are driven LOW and all DQS signals are driven HIGH. In adjust mode, BL = 4 of operation code data must be used. In case of OCD calibration default, output driver characteristics have a nominal impedance value of 18 Ohms during nominal temperature and voltage conditions. OCD applies only to normal full strength output drive setting defined by EMR (1) and if reduced strength is set, OCD default driver characteristics are not applicable. When OCD calibration adjust mode is used, OCD default output driver characteristics are not applicable. After OCD calibration is completed or driver strength is set to default, subsequent EMRS commands not intended to adjust OCD characteristics must specify A[9:7] as ‟000‟ in order to maintain the default or calibrated value. Table 1 – OCD Drive Mode Program A9 A8 A7 Operation 0 0 0 OCD calibration mode exit 0 0 1 Drive (1) DQ, DQS HIGH and DQS LOW 0 1 0 Drive (0) DQ, DQS LOW and DQS HIGH 1 0 0 Adjust mode 1 1 1 OCD calibration default 8.2.3.2 OCD Impedance Adjust To adjust output driver impedance, controllers must issue the ADJUST EMRS command along with a 4 bit burst code to DDR2 SDRAM as in table 2. For this operation, Burst Length has to be set to BL = 4 via MRS command before activating OCD and controllers must drive the burst code to all DQs at the same time. DT0 in table 2 means all DQ bits at bit time 0, DT1 at bit time 1, and so forth. The driver output impedance is adjusted for all DDR2 SDRAM DQs simultaneously and after OCD calibration, all DQs and DQS‟s of a given DDR2 SDRAM will be adjusted to the same driver strength setting. The maximum step count for adjustment is 16 and when the limit is reached, further increment or decrement code has no effect. The default setting may be any step within the 16 step range. When Adjust mode command is issued, AL from previously set value must be applied. Table 2 – OCD Adjust Mode Program 4 bit burst code inputs to all DQs Operation DT0 DT1 DT2 DT3 Pull-up driver strength Pull-down driver strength 0 0 0 0 NOP (No operation) NOP (No operation) 0 0 0 1 Increase by 1 step NOP 0 0 1 0 Decrease by 1 step NOP 0 1 0 0 NOP Increase by 1 step 1 0 0 0 NOP Decrease by 1 step 0 1 0 1 Increase by 1 step Increase by 1 step 0 1 1 0 Decrease by 1 step Increase by 1 step 1 0 0 1 Increase by 1 step Decrease by 1 step 1 0 1 0 Decrease by 1 step Decrease by 1 step Other Combinations Reserved |
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