When I configure a Virtex device using the iMPACT software, the status of the DONE pin is reported after configuration. How does this work?
To determine the status of the DONE pin, iMPACT checks the "Instruction Capture" value through JTAG.
The Instruction Capture value is placed in the Instruction Register whenever the JTAG TAP state machine is moved through the Capture-IR. The meaning of the Instruction Capture bits is defined in the BSDL file; one bit represents the status of the DONE pin.
ChipScope / JTAG Programmer
ChipScope and JTAG Programmer use an alternative method to check the status of the DONE pin: it checks the Device's Status Register.
If the BitGen option (disable Readback) is selected, the Status Register is not updated with the status of the DONE pin. In this case, JTAG Programmer reports that the status of the DONE pin cannot be determined.