NXP Semiconductors MPC5644A, Reference Manual, Page: 1691 / 1735

Nexus Port Controller (NPC)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 1691
37.5.7 Nexus reset control
The JCOMP input that is used as the primary reset signal for the NPC is also used by the NPC to generate
a single-bit reset signal for other Nexus blocks. If JCOMP is negated, an internal reset is asserted,
indicating that all Nexus modules should be held in reset.
37.5.8 System clock locked indication
Following a power-on reset, MDO[0] can be monitored to provide the lock status of the system clock.
MDO[0] is driven to a logic 1 until the system clock achieves lock after exiting power-on reset. Once the
system clock is locked, MDO[0] is negated and tools may begin Nexus configuration. Loss of lock
conditions that occur subsequent to the exit of power-on reset and the initial lock of the system clock do
not cause a Nexus reset, and therefore do not result in MDO[0] driven high.
37.6 Initialization/Application information
37.6.1 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 5001-2001 standard for more detail.