3 Measuring the Calibration Clock Frequency

In order for the calibration routine to provide an accurate result, the exact frequency of the calibration clock signal should be measured externally and provided to the calibration firmware. A basic way to accomplish this would be to connect an oscilloscope to the calibration clock line and simply include the measured value in the firmware source code.

The calibration clock signal should be transmitted on the JTAG TDI pin during calibration. To measure its frequency, simply initiate a calibration session with the tool to be used after connecting the JTAG interface to the target device. The calibration firmware is not required to run on the target device. The clock signal should then be available on the TDI line sufficiently long enough to be captured by an oscilloscope or other measurement device. The frequency of the calibration clock signal should be in the 32 kHz range.

If the calibration firmware is not running on the target device, the calibration command should return an error message, which can be ignored at this time.