
MOTOROLA
IEEE 1149.1 Test Access Port (JTAG)
20-1
Section 20
IEEE 1149.1 Test Access Port (JTAG)
The MCF5249 JTAG test architecture implementation currently supports circuit board test strategies that
are based on the IEEE standard. This architecture provides access to all of the data and chip control pins
from the board edge connector through the standard four-pin test access port (TAP) and the active-low
JTAG reset pin, TRST. The test logic uses static design and is wholly independent of the system logic,
except where the JTAG is subordinate to other complimentary test modes (see the DEBUG section, for
more information). When in subordinate mode, the JTAG test logic is placed in reset and the TAP pins can
be used for other purposes in accordance with the rules and restrictions set forth using a JTAG
compliance-enable pin.
The MCF5249 JTAG implementation can do the following:
Perform boundary-scan operations to test circuit board electrical continuity
Bypass the MCF5249 by reducing the shift register path to a single cell
Sample the MCF5249 system pins during operation and transparently shift out the result
Set the MCF5249 output drive pins to fixed logic values while reducing the shift register path to a
single cell
Protect the MCF5249 system output and input pins from backdriving and random toggling (such as
during in-circuit testing) by placing all system signal pins to high- impedance state
Note: The IEEE Standard 1149.1 test logic cannot be considered completely benign to
those planning not to use JTAG capability. Users must observe certain precautions
to ensure that this logic does not interfere with system or debug operation. Refer to
20.1
JTAG OVERVIEW
Figure 20-1 is a block diagram of the MCF5249 implementation of the 1149.1 IEEE Standard. The test
logic includes several test data registers, an instruction register, instruction register control decode, and a
16-state dedicated TAP controller.
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