SPRUJ53B April 2024 – September 2024 TMS320F28P550SJ , TMS320F28P559SJ-Q1
The TAP_STATUS register reflects the status of the JTAG TAP at any given time. Normally when no JTAG is connected to the device, the status can be IDLE. In some cases with excessive PCB noise, there can be unwanted TMS and TCK toggles that take JTAG out of the IDLE state. When persistent, this can ultimately lead to unwanted activation of the JTAG Boundary Scan or some other JTAG mode that can interfere with the intended application. To avoid this scenario, place strong enough pull resistors on the board to prevent noise from activating JTAG. As a debug tool, the TAP_STATUS register can be polled by the application code to detect if this is a cause of device disturbance. The SOFTPRES40[JTAG_nTRST] register can also be used to reset the JTAG TAP through software. Use this reset register with caution, as this prevents connecting a debugger unless the code qualifies writes to this register with some other GPIO state or other means to distinguish between noise and debugger accesses.
The TAP_CONTROL register can be used to disable the TAP state machine's control of the device. Using the TAP_CONTROL register can help to prevent noise from activating JTAG.