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AR# 40780

MIG Spartan-6 MCB - FPGA Input Termination Options


This section of the MIG Design Assistant focuses on FPGA Input Termination Options for Spartan-6 MCB designs.

Note: This Answer Record is part of the Xilinx MIG Solution Center (Xilinx Answer 34243).The Xilinx MIG Solution Center is available to address all questions related to MIG. Whether you are starting a new design with MIG or troubleshooting a problem, use the MIG Solution Center to guide you to the right information.


Optional on-chip termination features in Spartan-6 FPGAs eliminate complex external board termination schemes for high-speed single-ended signaling, such as those commonly found in memory interfaces. MIG provides several on-chip termination options for the bidirectional memory interface signals: dq, ldqs_p/n, udqs_p/n.

Calibrated Input Termination:

Provides calibrated on-die input termination for DDR2 and DDR3 memory interfaces. Calibration requires two extra pins to be added to the interface: RZQ and ZIO.This option sets the parameterCX_SKIP_IN_TERM_CAL=0 for the top-level MIG generated design, which enables the inputtermination calibration algorithm inthe mcb_soft_calibration module. In addition, the property IN_TERM=NONE is applied to the bidirectional memory interface signals in the MIG generated UCF.

See also:

(Xilinx Answer 34055)MIG Spartan-6 FPGA MCB - What are the requirements for the RZQ and ZIO pins?

Un-calibrated Input Termination:

Provides un-calibrated (approximated) on-die input termination resistod to VCCIO and GND for DDR2 and DDR3 memory interfaces.This option sets the parameterCX_SKIP_IN_TERM_CAL=1 for the top-level MIG generated design, whichdisables the inputtermination calibration algorithm inmcb_soft_calibration module.In addition, the property IN_TERM=UNTUNED_SPLIT_25/50/75 (based on the selection in MIG)is applied to the bidirectional memory interface signals in the MIG generated UCF.

Please checkthe"Internal Termination">"On-chip Termination" section ofthe Spartan-6 SelectIO Resources User Guide(UG381) for detailed information about uncalibrated on-die termination. IBIS simulation is recommended for all these situations.

See also:

(Xilinx Answer 37081)MIG Spartan-6 MCB - Calibrated Input Termination IBIS Simulation

Linked Answer Records

Associated Answer Records

AR# 40780
Date 12/15/2012
Status Active
Type General Article
  • Spartan-6 LX
  • Spartan-6 LXT
  • MIG