PXS20RM Datasheet, PDF (1143/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

34.6 Initialization/Application Information
Nexus Port Controller (NPC)
34.6.1 Accessing NPC tool-mapped registers
To initialize the TAP for Nexus register accesses, the following sequence is required:
1. Enable the Nexus TAP controller
2. Load the TAP controller with the NEXUS-ENABLE instruction
To write control data to NPC tool-mapped registers, the following sequence is required:
1. Write the 7-bit register index and set the write bit to select the register with a pass through the
SELECT-DR-SCAN path in the TAP controller state machine.
2. Write the register value with a second pass through the SELECT-DR-SCAN path. Note that the
prior value of this register is shifted out during the write.
To read status and control data from NPC tool-mapped registers, the following sequence is required:
1. Write the 7-bit register index and clear the write bit to select register with a pass through
SELECT-DR-SCAN path in the TAP controller state machine.
2. Read the register value with a second pass through the SELECT-DR-SCAN path. Data shifted in
is ignored.
See the IEEE-ISTO 5001-2003 standard for more detail.
Freescale Semiconductor
PXS20 Microcontroller Reference Manual, Rev. 1
34-19