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IEEE 1149.1 Test Access Port
MOTOROLA
MPC801 USER’S MANUAL
19-19
19
19.3.4 The clamp Instruction
The
clamp
instruction selects the single-bit bypass register as illustrated in Figure 19-7
above, and the state of all signals driven from the system output pins is completely defined
by the data previously shifted into the boundary scan register by using the
instruction.
sample/preload
19.3.5 The hi-z Instruction
The
hi-z
instruction is provided as a manufacturer’s optional public instruction to avoid back
driving the output pins during circuit board testing. When
(including the two-state drivers) are turned off (high impedance) and the instruction selects
the bypass register.
hi-z
is invoked, all output drivers
19.4 MPC801 RESTRICTIONS
The control afforded by the output enable signals using the boundary scan register and the
extest
instruction requires a compatible circuit board test environment to avoid
device-destructive configurations. You must avoid situations in which the MPC801 output
drivers are enabled into actively driven networks. The MPC801
cc
mode. The interaction of the scan chain interface with low-power stop mode has the
following characteristics:
features a low-power stop
The TAP controller must be in the test-logic-reset state to either enter or remain in the
low-power stop mode. Leaving the TAP controller in the test-logic-reset state negates
its ability to achieve low-power, but does not otherwise affect device functionality.
The TCK input is not disabled in low-power stop mode. To consume minimal power, the
TCK input should be externally connected to V
normal mode (nonscan chain).
The TMS, TDI, and TRST pins include on-chip pull-up resistors. In low-power stop
mode, these two pins should remain either unconnected or connected to V
minimal power consumption. For proper reset of the scan chain test logic, the best
approach is to pull active TRST at power-on reset. The easiest way to reset the scan
chain logic is to connect TRST to HRESET, SRESET, or PORESET.
CC
or ground while in low-power or
CC
to achieve
19.5 NONSCAN CHAIN OPERATION
In nonscan chain operation, there are two constraints. First, the TCK input does not include
an internal pull-up resistor and should be tied high or low to preclude mid-level inputs. The
second constraint is that the scan chain test logic must be kept transparent to the system
logic by forcing TAP into the test-logic-reset controller state by using one of two methods.
The first method is to connect the TRST pin to logic 0 (or one of the reset pins). The second
method is to assure the TMS pin is sampled as a logic one for five consecutive TCK rising
edges. If the TMS pin remains connected to V
CC
or does not change state,
then the TAP
controller cannot leave the test-logic-reset state, regardless of the TCK pin’s state.
19.6 MOTOROLA MPC801 BSDL DESCRIPTION
The BSDL file for exercising the scan chain logic on the MPC801 is available at the Motorola
web site (
www.mot.com/netcomm
) in the MPCxxx Embedded PowerPC area.