2.9.2. RTCK connections

This section describes the RTCK connections.

Global port and RTCK

When more than one bit of PORTSEL[7:0] is set, all active JTAG-AP multiplexor port RTCKs are combinatorially joined, so that:

  • If TCK=0 then select OR of active RTCKs

  • TCK=1 then select AND of active RTCKs.

An active RTCK is generated by an active port which is defined as a port which:

  • is selected, when its PORTSEL[7:0] bit is set

  • is connected, when its PORTCONNECTED[7:0] bit is set

  • has not been disabled or powered down in this session, when its PSTA bit is 0.

If no ports are active, RTCK is connected directly to TCK. This means that disabling or powering down a JTAG slave cannot lock up the RTCK interface.

Asynchronous TAP controllers which do not require an RTCK connection should connect their TCK output from JTAG-AP to the corresponding RTCK input.

RTCK wrapper

Note

This section applies only to synchronous TAP controllers.

Where devices do not have a return clock, a RTCK wrapper must be used to register TCK against the processor clock. See the CoreSight Components Implementation Guide and the applicable Integration Manual for details on how to implement an RTCK wrapper.

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