EtronTech
EM68916CWQA
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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
drive 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. Output driver characteristics for OCD calibration default are specified
in the following table. OCD applies only to normal full strength output drive setting defined by EMRS and if
half 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 A7~A9 as ’000’ in order to maintain the default or calibrated value.
Table 9.OCD drive mode program
A9
A8
A7
operation
0
0
0
1
1
0
0
1
0
1
0
1
0
0
1
OCD calibration mode exit
Drive(1) DQ, DQS, HIGH and DQS# LOW
Drive(0) DQ, DQS, LOW and DQS# HIGH
Adjust mode
OCD calibration default
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OCD impedance adjust
To adjust output driver impedance, controllers must issue the ADJUST EMRS command along with a 4bit
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 this burst code to all DQs at the
same time. DT0 in the following 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 is 16 and when the limit is reached, further increment or
decrement code has no effect. The default setting maybe any step within the 16 step range. When Adjust
mode command is issued, AL from previously set value must be applied.
Table 10.OCD adjust mode program
4bit burst code inputs to all DQs
Operation
Pull-down driver strength
DT0
0
DT1
0
DT2
0
DT3
0
Pull-up driver strength
NOP
NOP
0
0
0
1
0
0
1
1
0
0
1
0
1
1
0
0
0
1
0
0
0
1
0
1
1
0
0
0
1
0
1
0
Increase by 1 step
Decrease by 1 step
NOP
NOP
NOP
Increase by 1 step
Decrease by 1 step
Increase by 1 step
Increase by 1 step
Decrease by 1 step
Decrease by 1 step
NOP
Increase by 1 step
Decrease by 1 step
Increase by 1 step
Decrease by 1 step
Other Combinations
Reserved
Etron Confidential
14
Rev. 1.1
Apr. 2009
ETRON [ ETRON TECHNOLOGY, INC. ]
