What is the strength of the internal pull-up or pull-down resistors in the Spartan-3 I/O block?
The strength of the internal pull-up and pull-down resistors is defined by the parameters Irpu and Irpd in the Spartan-3 FPGA Family Data Sheet (DS099), found at:
To obtain the values of the pull-up and pull-down resistors, use following equation:
Pulldown resistor: Rrpd = Vcc / Irpd
Pullup resistor: Rrpu = Vcc / Irpu