The actual TCK frequency has dependency on factors such as PC speed, parallel port vs. USB cable, USB 1.1 vs. 2.0 etc.
Under ispVM Project -> Project Settings, Advanced, user may use the TCK Low Pulse Width Delay option to slow down the TCK.
This option delays the low pulse width as follows:
- setting TCK Low Pulse Width Delay to 2 will stretch the low pulse approximately twofold.
- setting TCK Low Pulse Width Delay to 3 will stretch the low pulse approximately threefold.
However, the setting is not exact which means the exact ratio, like the frequency, will vary from system to system. It is simply a tool for user to leverage for debug programming issues due to noise. It is not meant to provide exact frequency or duty cycle control.
Take note that user should not stretch the high pulse of the TCK on the parallel port because some PCs will create a glitch doing so and the device will see a double clock edge.
Separate duty cycle control is not available.