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The Port Status register captures the state of a connected and selected port on every clock cycle. If a connected and selected port is disabled or powered down, that is signal port_enabled goes low, even transiently, the corresponding bit in the PSTA register is set in the next cycle. It remains 1 until it is cleared by writing 1 to it. It gets cleared automatically on abort. Deselecting a port in PSEL does not alter the state of PSTA. If the PSTA bit is set for a port, that port is disabled and its TCK, TMS, and TDI outputs are driven LOW until its PSTA bit is cleared. Software must not clear any PSTA bit unless the JTAG-AP is idle, that is CSW.SERACTV=
0b0 and CSW.WFIFOCNT=
The PSTA register characteristics are:
The following figure shows the bit assignments.
The following table shows the bit assignments.
Table 9-146 PSTA register bit assignments
Read-As-Zero, Writes Ignored.
Port Status. Each register field is named as PSTAn, where n = 0-7. The numerical index represents the bit position of that field in this register.