NXP Semiconductors MPC5644A Reference Manual page 1689

Table 37-11. Loading NEXUS-ENABLE instruction (continued)
Clock TMS
13 1
14 0
37.5.3.4 Selecting a Nexus client register
When the NEXUS-ENABLE instruction is decoded by the TAP controller, the input port allows
development tool access to all Nexus registers. Each register has a 7-bit address index.
All register access is performed via the SELECT-DR-SCAN path. The Nexus Controller defaults to the
REG_SELECT state when enabled. Accessing a register requires two passes through the
SELECT-DR-SCAN path: one pass to select the register and the second pass to read/write the register.
The first pass through the SELECT-DR-SCAN path is used to enter an 8-bit Nexus command consisting
of a read/write control bit in the LSB followed by a 7-bit register address index, as illustrated in
Figure 37-11. The read/write control bit is set to 1 for writes and 0 for reads.
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,
there is no requirement to shift out the entire register contents. Shifting may be terminated once the
required number of bits have been acquired.
Table 37-12 illustrates a sequence which writes a 32-bit value to a register
Clock TMS
0 0
1 1 SELECT-DR-SCAN
2 0
3 0
12 1
13 1
14 1 SELECT-DR-SCAN
15 0
Freescale Semiconductor
IEEE 1149.1 state Nexus state
UPDATE-IR IDLE
RUN-TEST/IDLE REG_SELECT
MSB
7-bit register index
Figure 37-11. IEEE 1149.1 controller command input
Table 37-12. Write to a 32-bit Nexus client register
IEEE 1149.1 state Nexus state
RUN-TEST/IDLE REG_SELECT
REG_SELECT
CAPTURE-DR REG_SELECT
SHIFT-DR REG_SELECT
7 TCKs
EXIT1-DR REG_SELECT
UPDATE-DR REG_SELECT
DATA_ACCESS Second pass through SELECT-DR-SCAN path
CAPTURE-DR DATA_ACCESS Internal shifter loaded with current value of register
MPC5644A Microcontroller Reference Manual, Rev. 6
Description
NEXUS-ENABLE loaded into instruction register
Ready to be read/write Nexus registers
LSB
R/W
Description
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.
Last bit of register index shifted into TDI
Controller decodes and selects register
Nexus Port Controller (NPC)
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