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AR# 38410

Virtex-5 FPGA GTP/GTX Transceiver - What is the RX impedance value before and after power up and configuration?


The Virtex-5 FPGA GTP/GTX Transceivers are at certain impedance levels depending on before or after power up, andbefore or after configuration. This is importantfor certain protocols such as PCI-Express that relies on the impedanceto detect the receiver. This Answer Record discusses the RX impedance values for these different cases.


In protocols such as PCI-Express, the other endwould attempt to detect the impedance ofreceiver and start the link initialization process if a valid impedance is detected at the receiver end. Therefore, it is important to know the impedancethe Virtex-5 FPGA GTP/GTX receivers will show before and after power up, and configuration.
The impedance values are measured for these different cases using TDR. The impedance measurement results are as follows:
  • The RX is at a high impedance in an unpowered state.
  • Whenpowered on, but beforethe device is configured, the RX is at a high impedance.
  • After configuration, the RX is at 50 Ohm impedance.
AR# 38410
Date 12/15/2012
Status Active
Type General Article
  • Virtex-5 LXT
  • Virtex-5 SXT
  • Virtex-5 FXT
  • Virtex-5 TXT