Get Max TCK

Click the Get Max TCK button in the Chain Operations section to find the maximum TCK frequency for the circuit under test, using the current pin mapping. The result is displayed in the TCK Frequency text box next it. In XJDeveloper, XJInvestgator or when an XJPack file is opened in JTAG Chain Debugger this TCK frequency text box is not present. Instead, if Get Max TCK succeeds, the user is prompted to update the project frequency with either the found maximum frequency or the lowest of the frequencies defined in the BSDL files of the devices in the chain (choosing the lower of the two).

Optimised scans

When running this operation on a project that uses the Optimised scans feature, each subchain will be tested one at a time in isolation. If this succeeds, the user is prompted to update the TCK frequencies for each subchain, with either the found maximum frequency or the lowest of the frequencies defined in the BSDL files of the devices in the subchain (choosing the the lower of the two).

For profiles with multiple subchains, attempting to run one or more of those subchains at their found maximum frequencies may cause the chain to break, due to interference between the chains. This may be more noticeable at higher TCK frequencies, and will be dependent on the board layout and connections. In this case one or more of the subchain TCK frequencies may need to be reduced. The Signal Integrity feature should be used to determine if a given profile can run reliably with the chosen subchain TCK frequencies.