eorex

EM44AM1684LBA

Jul. 2006

www.eorex.com

OCD impedance adjust

To adjust output driver impedance, controllers must issue the ADJUST EMRS(1) command along with a 4 bit

burst code to DDR2 SDRAM as in the following table. 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 is the table 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 of a

given DDR2 SDRAM will be adjusted to the same driver strength setting. The maximum step count for

adjustment can be up to 16 and when the limit is reached, further increment or decrement code has no

effect. The default setting may be any step within the maximum step count range. When Adjust mode

command is issued, AL from previously set value must be applied.

Off-Chip-Driver Adjust Program

4 bit burst code inputs to all DQs

Operation

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

Reserved

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