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How do I determine the maximum test clock (TCK) frequency of the boundary scan device?

The boundary scan device test clock (TCK) information is described in the boundary scan description language (BSDL) at the TAP port identification which assigns a special meaning to these signals.

Attribute TAP_SCAN_CLOCK of TCK : signal is (20.0e6, BOTH)
Note: The 20.0e6 is a 20 Mhz clock frequency.
This means that the TCK frequency setting can be set up to 20 MHz during boundary scan testing of the device. However, do take note that the TCK frequency in a chain has to be set to the lowest freqency of a device in a chain.