The TCK and TMS signals go to all devices in the chain. Consequently,
their signal quality is important. For example, TCK
should transition monotonically at all receivers to ensure proper JTAG functionality and
must be properly terminated. The quality of TCK can
limit the maximum frequency for reliable JTAG configuration.
Additionally, if the chain is large (three
devices or more), TMS and TCK should be buffered to ensure that they have sufficient drive strength
at all receivers, and the voltage at logic High must be compatible with all devices in
the chain.
When interfacing to devices from other
manufacturers, optional JTAG signals can be present (such as TRST and enables) and might need to be driven.