
Chapter 8. Signal Descriptions
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Non-Protocol Signal Descriptions
8.5.6.3 JTAG Test Data Output (TDO)Output
The JTAG test data output signal is an output on the MPC7400. Following is the state
meaning for the TDO output signal.
State Meaning
Asserted/NegatedThe contents of the selected internal instruction
or data register are shifted out onto this signal on the falling edge of
TCK. The TDO signal remains in a high-impedance state except
when scanning of data is in progress.
8.5.6.4 JTAG Test Mode Select (TMS)Input
The test mode select (TMS) signal is an input on the MPC7400. Following is the state
meaning for the TMS input signal.
State Meaning
Asserted/NegatedThis signal is decoded by the internal JTAG TAP
controller to distinguish the primary operation of the test support
circuitry.
Note that this input contains an internal pull-up resistor to ensure that
an unterminated input appears as a high signal level to the test logic.
8.5.6.5 JTAG Test Reset (TRST)Input
The test reset (TRST) signal is an input on the MPC7400. Following is the state meaning
for the TRST input signal.
State Meaning
AssertedThis input causes asynchronous initialization of the
internal JTAG test access port controller. Note that the signal must be
asserted during the assertion of HRESET in order to properly
initialize the JTAG test access port.
NegatedIndicates normal operation.
Note that this input contains an internal pull-up resistor to ensure that
an unterminated input appears as a high signal level (negated) to the
test logic.
8.5.7 Bus Voltage Select (BVSEL)/L2 Voltage Select
(L2VSEL)
The MPC7400 provides several I/O voltages to support both compatibility with existing
systems and migration to future systems. See the MPC7400 hardware specification for
more information on the BVSEL and L2VSEL signals, which control various I/O voltage
options.