NXP Semiconductors MPC5644A, Reference Manual, Page: 1667 / 1735

JTAG Controller (JTAGC)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 1667
36.5.4.1 IDCODE instruction
IDCODE selects the 32-bit device identification register as the shift path between TDI and TDO. This
instruction allows interrogation of the MCU to determine its version number and other part identification
data. IDCODE is the instruction placed into the instruction register when the JTAGC block is reset.
36.5.4.2 SAMPLE/PRELOAD instruction
The SAMPLE/PRELOAD instruction has two functions:
• First, the SAMPLE portion of the instruction obtains a sample of the system data and control
signals present at the MCU input pins and just before the boundary scan register cells at the output
pins. This sampling occurs on the rising edge of TCK in the Capture-DR state when the
SAMPLE/PRELOAD instruction is active. The sampled data is viewed by shifting it through the
boundary scan register to the TDO output during the Shift-DR state. Both the data capture and the
shift operation are transparent to system operation.
• Secondly, the PRELOAD portion of the instruction initializes the boundary scan register cells
before selecting the EXTEST or CLAMP instructions to perform boundary scan tests. This is
achieved by shifting in initialization data to the boundary scan register during the Shift-DR state.
The initialization data is transferred to the parallel outputs of the boundary scan register cells on
the falling edge of TCK in the Update-DR state. The data is applied to the external output pins by
the EXTEST or CLAMP instruction. System operation is not affected.
36.5.4.3 SAMPLE instruction
The SAMPLE instruction obtains a sample of the system data and control signals present at the MCU input
pins and just before the boundary scan register cells at the output pins. This sampling occurs on the rising
edge of TCK in the Capture-DR state when the SAMPLE instruction is active. The sampled data is viewed
by shifting it through the boundary scan register to the TDO output during the Shift-DR state. There is no
defined action in the Update-DR state. Both the data capture and the shift operation are transparent to
system operation.
36.5.4.4 EXTEST—external test instruction
EXTEST selects the boundary scan register as the shift path between TDI and TDO. It allows testing of
off-chip circuitry and board-level interconnections by driving preloaded data contained in the boundary
scan register onto the system output pins. Typically, the preloaded data is loaded into the boundary scan
BYPASS 11111 Selects bypass register for data operations
Factory debug reserved 00101, 00110,
01010, 00111
Intended for factory debug only
Reserved
1
All other opcodes Decoded to select bypass register
1
The manufacturer reserves the right to change the decoding of reserved instruction codes in the future.
Table 36-7. JTAG Instructions (continued)
Instruction Code[4:0] Instruction summary