In the Virtex-II/-II Pro User Guide, Rule #3 states that VRN must be pulled up to VCCO, while VRP must be pulled down to GND. Is this correct?
You can access this information in the Virtex-II and Virtex-II Pro User Guides by selecting "Design Considerations" -> Using Digitally Controlled Impedance (DCI) -> DCI in Virtex-II (Virtex-II Pro) Hardware:
1. Go to:
2. Select Virtex-II Pro under "FPGA Device Families."
3. Select Virtex-II Pro Platform FPGA User Guide.
Yes, the user guides are correct.
"P" is for the PMOS transistor's impedance. The resistor that controls the pull-up impedance of PMOS must be connected to the ground pin. Therefore, VRP must be pulled down to GND.
"N" is for the NMOS transistor's impedance. The resistor that controls the pull-down impedance of NMOS must be connected to VCCO. Therefore, VRN is pulled up to VCCO.