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Functional Description
contains the $2 opcode. The sampled data is accessible by shifting it through the
boundary scan register to the TDO output by using the shift-DR state. Both the data
capture and the shift operation are transparent to system operation.
External synchronization is required to achieve meaningful
results because there is no internal synchronization between
TCLK and the system clock.
• PRELOAD - initialize the boundary scan register update cells before selecting
EXTEST or CLAMP. This is achieved by ignoring the data shifting out on the TDO
pin and shifting in initialization data. The update-DR state and the falling edge of
TCLK can then transfer this data to the update cells. The data is applied to the
external output pins by the EXTEST or CLAMP instruction.
31.5.3.4 TEST_LEAKAGE Instruction
The TEST_LEAKAGE instruction forces the jtag_leakage output signal to high. It is
intended to tri-state all output pad buffers and disable all of the part's pad input buffers
except TEST and TRST. The jtag_leakage signal is asserted at the rising edge of TCLK
when the TAP controller transitions from update-IR to run-test/idle state. Once asserted, the
part disables the TCLK, TMS, and TDI inputs into JTAG and forces these JTAG inputs to
logic 1. The TAP controller remains in the run-test/idle state until the TRST input is
asserted (logic 0).
31.5.3.5 ENABLE_TEST_CTRL Instruction
The ENABLE_TEST_CTRL instruction selects a 3-bit shift register (TEST_CTRL) for
connection as a shift path between the TDI and TDO pin. When the user transitions the TAP
controller to the UPDATE_DR state, the register transfers its value to a parallel hold
register. It allows the control chip to test functions independent of the JTAG TAP controller
state.
31.5.3.6 HIGHZ Instruction
The HIGHZ instruction eliminates the need to backdrive the output pins during
circuit-board testing. HIGHZ turns off all output drivers, including the 2-state drivers, and
selects the bypass register. HIGHZ also asserts internal reset for the MCU system logic to
force a predictable internal state.
31.5.3.7 LOCKOUT_RECOVERY Instruction
If a user inadvertently enables security on a MCU, the LOCKOUT_RECOVERY
instruction allows the disabling of security by the complete erasure of the internal flash
contents including the configuration field. This does not compromise security as the entire
31-10
NOTE
MCF5282 User's Manual
MOTOROLA
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