Datasheet

-
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 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
-
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.
D
T0
in the following table means all DQ bits at bit time 0, D
T1
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
D
T0
D
T1
D
T2
D
T3
Pull-up driver strength Pull-down driver strength
0 0 0 0 NOP NOP
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
AS4C32M16D2A-25BIN
Alliance Memory Inc.
511 Taylor Way, San Carlos, CA 94070 TEL: [phone] FAX: [phone]
Alliance Memory Inc. reserves the right to change products or specification without notice
Rev.1.2
14
Jun./2014