MPC5604B/C Microcontroller Reference Manual, Rev. 8
794 Freescale Semiconductor
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 can be terminated after fetching the required number of bits.
32.8.4 JTAGC instructions
This section gives an overview of each instruction, refer to the IEEE 1149.1-2001 standard for more
details.
The JTAGC implements the IEEE 1149.1-2001 defined instructions listed in Table 32-3.
32.8.4.1 BYPASS instruction
BYPASS selects the bypass register, creating a single-bit shift register path between TDI and TDO.
BYPASS enhances test efficiency by reducing the overall shift path when no test operation of the MCU is
required. This allows more rapid movement of test data to and from other components on a board that are
required to perform test functions. While the BYPASS instruction is active the system logic operates
normally.
Table 32-3. JTAG Instructions
Instruction Code[4:0] Instruction Summary
IDCODE 00001 Selects device identification register for shift
SAMPLE/PRELOAD 00010 Selects boundary scan register for shifting, sampling, and
preloading without disturbing functional operation
SAMPLE 00011 Selects boundary scan register for shifting and sampling without
disturbing functional operation
EXTEST 00100 Selects boundary scan register while applying preloaded values to
output pins and asserting functional reset
ACCESS_AUX_TAP_TCU 11011 Grants the TCU ownership of the TAP
ACCESS_AUX_TAP_ONCE 10001 Grants the PLATFORM ownership of the TAP
ACCESS_AUX_TAP_NPC 10000 Grants the Nexus port controller (NPC) ownership of the TAP
Reserved 10010 —
BYPASS 11111 Selects bypass register for data operations
Factory Debug Reserved
1
1
Intended for factory debug, and not customer use
00101
00110
01010
Intended for factory debug only
Reserved
2
2
Freescale reserves the right to change the decoding of reserved instruction codes
All other codes Decoded to select bypass register
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