Article ID: 000078621 Content Type: Troubleshooting Last Reviewed: 08/27/2013

Can I use calibrated 40 or 60 ohm series OCT values on bidirectional pins when using calibrated 50 ohm parallel OCT in Stratix III and Stratix IV devices?



No, as stated in I/O Features in Stratix III Devices (PDF) and I/O Features in Stratix IV Devices (PDF), when using calibrated input parallel and calibrated output series termination on bidirectional pins, they must use the same termination value because each I/O pin can only reference one on chip termination (OCT) calibration block.

However, the Quartus® II software allows you to select different series OCT with calibration values for the same bidirectional pin that you assign parallel 50 ohm OCT with calibration. 

For example, you can set the output series termination to be series 40 ohm or 60 ohm with calibration, and set the input termination to be parallel 50 ohm with calibration.  This will compile successfully in the Quartus II software, but the output series termination will calibrate to the resistor value connected to the Rup and Rdn pins. 

Parallel OCT is only supported with 50 ohms in Stratix® III and Stratix IV devices, thus bidirectional pins using 50 ohm parallel OCT with calibration for the input operation will also use 50 ohm series OCT with calibration for output operations (the only exception is when using calibrated 25 ohm series OCT with left-shift series termination).  If you choose 40 ohm or 60 ohm series OCT in this example, the power and timing models use those values, but the device will calibrate to the 50 ohm value that matches the Rup and Rdn pins.

Related Products

This article applies to 4 products

Stratix® IV E FPGA
Stratix® IV GT FPGA
Stratix® IV GX FPGA
Stratix® III FPGAs



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