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TMS320C6678: DDR3: Un-used upper byte, ECC

erez cohen
Intellectual 595 points
Part Number: TMS320C6678

Hello,
on my design x16 DDR3 is used for ECC.

on the EVB the unused byte is connected as follow:

DQSU 1.5V

DQSUn GND, via 4.7K

DMU GND, via 4.7K

According my understanding the following should be done (refer Micron notes below):

DQSU should be ‘0’

DQSUn should be 1.5V

DMU should be 1.5V

according Micron Notes:

A x16 device's DQ bus is comprised of two bytes. If only one of the bytes needs to be used, use the lower byte for data transfers and terminate the upper byte as noted:
– Connect UDQS to ground via 1kΩ* resistor.
– Connect UDQS# to VDD via 1kΩ* resistor.
– Connect UDM to VDD via 1kΩ* resistor.
– Connect DQ[15:8] individually to either VSS, VDD, or VREF via 1kΩ resistors,* or float DQ[15:8]. *If ODT is used, 1kΩ resistor should be changed to 4x that of the selected ODT

please advise how to connect.

thanks,

Erez

  • 0
    TI__Mastermind 46460 points

    Erez,

    You are asking about the terminations on the unused pins on the SDRAM device.  You should always follow the recommendations from the device's datasheet.  Their recommendations will be optimal for their device.  The recommendations that we provide for this device topology are generalized, but not necessarily optimum.

    Tom