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Adventurer
Adventurer
985 Views
Registered: ‎10-22-2017

What are the explanations of differences between DDR ODT and DCI?

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What are the explanations of differences between DDR ODT and DCI?
Both functions are used for impedance matching, DCI is used for impedance matching at the receiving end, and ODT is used for impedance matching at the sending end. Do I understand this correctly?

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Moderator
Moderator
1,222 Views
Registered: ‎11-28-2016

Re: What are the explanations of differences between DDR ODT and DCI?

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Hello @caoshouqi,

 

DCI is used to make sure the FPGA driver and termination impedances are always at their expected value during operation and accounts for any process variation in the device as well as temperature and voltage changes.  This is derived from internal logic and the 240-ohm resistor connected on the VRP pin.

 

ODT is the actual termination value at the receiver on the DDR interface.  The DDR device derives this from a mode register setting and the 240-Ohm ZQ resistor.  Also worth noting that DDR devices do have ZQ calibration to make sure it adjusts for temperature and voltage changes.  The FPGA derives this from the IP settings and is constantly adjusted to remain accurate with the DCI feature.

 

Wrapping this together, when the FPGA needs to have 40-ohm ODT enabled during a read, DCI makes sure the the resistance present at the FPGA receivers is 40-ohms.

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Moderator
Moderator
1,223 Views
Registered: ‎11-28-2016

Re: What are the explanations of differences between DDR ODT and DCI?

Jump to solution

Hello @caoshouqi,

 

DCI is used to make sure the FPGA driver and termination impedances are always at their expected value during operation and accounts for any process variation in the device as well as temperature and voltage changes.  This is derived from internal logic and the 240-ohm resistor connected on the VRP pin.

 

ODT is the actual termination value at the receiver on the DDR interface.  The DDR device derives this from a mode register setting and the 240-Ohm ZQ resistor.  Also worth noting that DDR devices do have ZQ calibration to make sure it adjusts for temperature and voltage changes.  The FPGA derives this from the IP settings and is constantly adjusted to remain accurate with the DCI feature.

 

Wrapping this together, when the FPGA needs to have 40-ohm ODT enabled during a read, DCI makes sure the the resistance present at the FPGA receivers is 40-ohms.

Adventurer
Adventurer
931 Views
Registered: ‎10-22-2017

Re: What are the explanations of differences between DDR ODT and DCI?

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Hi Ryana

 

Thank you for your answer so that I already understand!Thankyou!

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