Microcontroller User's Manual

MOTOROLA Chapter 31. IEEE 1149.1 Test Access Port (JTAG) 31-9
Functional Description
31.5.3.1 External Test Instruction (EXTEST)
The EXTEST instruction selects the boundary scan register. It forces all output pins and
bidirectional pins configured as outputs to the values preloaded with the
SAMPLE/PRELOAD instruction and held in the boundary scan update registers. EXTEST
can also configure the direction of bidirectional pins and establish high-impedance states
on some pins. EXTEST asserts internal reset for the MCU system logic to force a
predictable internal state while performing external boundary scan operations.
31.5.3.2 IDCODE Instruction
The IDCODE instruction selects the 32-bit IDCODE register for connection as a shift path
between the TDI and TDO pin. This instruction allows interrogation of the MCU to
determine its version number and other part identification data. The shift register LSB is
forced to logic 1 on the rising edge of TCLK following entry into the capture-DR
state.Therefore, the first bit to be shifted out after selecting the IDCODE register is always
a logic 1. The remaining 31 bits are also forced to fixed values on the rising edge of TCLK
following entry into the capture-DR state.
IDCODE is the default instruction placed into the instruction register when the TAP resets.
Thus, after a TAP reset, the IDCODE register is selected automatically.
31.5.3.3 SAMPLE/PRELOAD Instruction
The SAMPLE/PRELOAD instruction has two functions:
• SAMPLE - obtain a sample of the system data and control signals present at the
MCU input pins and just before the boundary scan cell at the output pins. This
sampling occurs on the rising edge of TCLK in the capture-DR state when the IR
TEST_LEAKAGE
1, 2
0101 Selects bypass register while tri-stating all output pins and assert to high the
jtag_leakage signal
ENABLE_TEST_CTRL 0110 Selects TEST_CTRL register
HIGHZ 1001 Selects bypass register while tri-stating all output pins and asserting functional reset
LOCKOUT_RECOVERY 1011 Allows for the erase of the TFM flash when the part is secure
CLAMP 1100 Selects bypass while applying fixed values to output pins and asserting functional
reset
BYPASS 1111 Selects bypass register for data operations
Reserved all others Decoded to select bypass register
3
1
Instruction for manufacturing purposes only
2
TRST pin assertion or power-on reset is required to exit this instruction.
3
Motorola reserves the right to change the decoding of the unused opcodes in the future.
Table 31-5. JTAG Instructions (continued)
Instruction IR[3:0] Instruction Summary