I want to run my cable at the fastest setting of 24 MHz, but iMPACT issues an error at the higher frequencies. All of my devices will not operate at the higher frequencies. Why?
The maximum TCK frequency can vary between Xilinx families. Not all devices support a TCK frequency of 24 MHz. You can identify the maximum TCK frequency by inspecting the BSDL file of the device in question, as shown in the following examples:
BSDL file for a Spartan device:
attribute TAP_SCAN_CLOCK of TCK : signal is (2.0e6, LOW);
BSDL file for a Virtex-II Pro device:
attribute TAP_SCAN_CLOCK of TCK : signal is (33.0e6, BOTH).
These files indicate that the maximum TCK frequency for the Spartan device is 2 MHz (which is a conservative number), and the Virtex-II Pro frequency is 33 MHz.
If the Platform Cable USB frequency is higher than the maximum TCK frequency reported in the BSDL file, the device might still be able to perform all JTAG operations; if not, the most common error reported is:
"ERROR:iMPACT:1210 - '1':Boundary-scan chain test failed at bit position '1'."
Lowering the cable frequency should resolve this error.