PXN20RM Datasheet, PDF (1172/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Nexus Development Interface (NDI)
The second pass through the SELECT-DR-SCAN path is used to read or write the register data by shifting
in the data (LSB first) during the SHIFT-DR state. When reading a register, the register value is loaded into
the IEEE 1149.1-2001 shifter during the CAPTURE-DR state. When writing a register, the value is
loaded from the IEEE 1149.1-2001 shifter to the register during the UPDATE-DR state. When reading
a register, no requirement exists to shift out the entire register contents. Shifting may be terminated once
the required number of bits have been acquired.
Table 36-12 illustrates a sequence that writes a 32-bit value to a register.
Table 36-12. Write to a 32-Bit Nexus Client Register
Clock
0
1
2
TMS
0
1
0
3
0
11
1
12
1
13
1
14
0
15
0
47
1
48
1
49
0
IEEE 1149.1 State
RUN-TEST/IDLE
SELECT-DR-SCAN
CAPTURE-DR
SHIFT-DR
7 TCKs
EXIT1-DR
UPDATE-DR
SELECT-DR-SCAN
CAPTURE-DR
SHIFT-DR
31 TCKs
EXIT1-DR
UPDATE-DR
RUN-TEST/IDLE
Nexus State
Description
REG_SELECT
REG_SELECT
REG_SELECT
REG_SELECT
IEEE 1149.1-2001 TAP controller in idle state
First pass through SELECT-DR-SCAN path
Internal shifter loaded with current value of controller
command input.
TDO becomes active, and write bit and 6 bits of register
index shifted in.
REG_SELECT Last bit of register index shifted into TDI
REG_SELECT Controller decodes and selects register
DATA_ACCESS Second pass through SELECT-DR-SCAN path
DATA_ACCESS Internal shifter loaded with current value of register
DATA_ACCESS TDO becomes active, and outputs current value of register
while new value is shifted in through TDI
DATA_ACCESS Last bit of current value shifted out TDO. Last bit of new
value shifted in TDI.
DATA_ACCESS Value written to register
REG_SELECT Controller returned to idle state. It could also return to
SELECT-DR-SCAN to write another register.
36.5.5.2.4 Nexus Auxiliary Port Sharing
Each of the Nexus modules on the MCU implements a request/grant scheme to arbitrate for control of the
Nexus auxiliary port when Nexus data is ready to be transmitted.
All modules arbitrating for the port are given fixed priority levels relative to each other. If multiple
modules have the same request level, this priority level is used as a tie-breaker. To avoid monopolization
of the port, the module given the highest priority level alternates following each grant. Immediately out of
reset the order of priority, from highest to lowest, is: NPC, Nexus3+, and Nexus2+. This arbitration
mechanism is controlled internally and is not programmable by tools or the user.
36.5.5.2.5 Nexus JTAG Port Sharing
Each of the individual Nexus modules on the device implements a TAP controller for accessing its
registers. When JCOMP is asserted, only the module whose ACCESS_AUX_TAP instruction is loaded
36-22
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor