MPC563XM Reference Manual, Rev. 1
Freescale Semiconductor
1379
Preliminary—Subject to Change Without Notice
32.5.3.4
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
. 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.
illustrates a sequence which writes a 32-bit value to a register
MSB
LSB
7-bit register index
R/W
Figure 32-11. IEEE 1149.1 Controller Command Input
Table 32-12. 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
12
1
EXIT1-DR
REG_SELECT
Last bit of register index shifted into TDI
13
1
UPDATE-DR
REG_SELECT
Controller decodes and selects register
14
1
SELECT-DR-SCAN
DATA_ACCESS
Second pass through SELECT-DR-SCAN path
15
0
CAPTURE-DR
DATA_ACCESS
Internal shifter loaded with current value of register
16
0
SHIFT-DR
DATA_ACCESS
TDO becomes active, and outputs current value of
register while new value is shifted in through TDI
31 TCKs
48
1
EXIT1-DR
DATA_ACCESS
Last bit of current value shifted out TDO. Last bit of
new value shifted in TDI.
49
1
UPDATE-DR
DATA_ACCESS
Value written to register
50
0
RUN-TEST/IDLE
REG_SELECT
Controller returned to idle state. It could also return
to SELECT-DR-SCAN to write another register.