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Nexus Development Interface (NDI)
PXN20 Microcontroller Reference Manual, Rev. 1
36-22
Freescale Semiconductor
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.
illustrates a sequence that writes a 32-bit value to a 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, , and . 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
Table 36-12. Write to a 32-Bit Nexus Client Register
Clock
TMS
IEEE 1149.1 State
Nexus State
Description
0
0
RUN-TEST/IDLE
REG_SELECT
IEEE 1149.1-2001 TAP controller in idle state
1
1
SELECT-DR-SCAN
REG_SELECT
First pass through SELECT-DR-SCAN path
2
0
CAPTURE-DR
REG_SELECT
Internal shifter loaded with current value of controller
command input.
3
0
SHIFT-DR
REG_SELECT
TDO becomes active, and write bit and 6 bits of register
index shifted in.
7 TCKs
11
1
EXIT1-DR
REG_SELECT
Last bit of register index shifted into TDI
12
1
UPDATE-DR
REG_SELECT
Controller decodes and selects register
13
1
SELECT-DR-SCAN
DATA_ACCESS
Second pass through SELECT-DR-SCAN path
14
0
CAPTURE-DR
DATA_ACCESS
Internal shifter loaded with current value of register
15
0
SHIFT-DR
DATA_ACCESS
TDO becomes active, and outputs current value of register
while new value is shifted in through TDI
31 TCKs
47
1
EXIT1-DR
DATA_ACCESS
Last bit of current value shifted out TDO. Last bit of new
value shifted in TDI.
48
1
UPDATE-DR
DATA_ACCESS
Value written to register
49
0
RUN-TEST/IDLE
REG_SELECT
Controller returned to idle state. It could also return to
SELECT-DR-SCAN to write another register.
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