Each bit in the register represents one of the virtual stimulus registers. When the bit is set, a pulse is sent on TRIGOUT when writing to the corresponding Stimulus Register. The pulse is held until TRIGOUTACK is returned, which can result in masking of multiple triggers with one acknowledgement. Triggers are not generated if trace is disabled. When secure non-invasive debug, or secure trace, is disabled, no triggers are generated for Stimulus Registers 16 to 31. If non-secure non-invasive debug, or trace, is disabled, no triggers are generated. The register is zero on reset, and the default is no triggers generated.

Table 12.7 shows the Trace Trigger Register bit assignments.

Figure 12.6 shows two writes to the stimulus port. It shows the timing for generating TRIGOUT and deasserting TRIGOUT with TRIGOUTACK. PENABLE and PREADY show when a write happens to the Stimulus Register.

The write at T0-T2 causes the TRIGOUT. This is acknowledged at T5. A write at T2-T4 generates another TRIGOUT. If the TRIGOUTACK stays HIGH beyond T6, this TRIGOUT is also acknowledged at T6. In the example TRIGOUTACK goes LOW before T6, so another TRIGOUTACK is required.