EM68A16CBQC
EtronTech
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
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
Rev. 1.1
14
Jan. /2016
ETRON [ ETRON TECHNOLOGY, INC. ]
