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1.7
Target Voltage Reference (VTREF) signals
The Target Voltage Reference, or VTREF, signals are used by DSTREAM-ST to determine the correct
logic levels of all inputs and outputs of the debug and trace interface.
To work with debug and trace interfaces on differing voltage rails, the DSTREAM-ST unit supports
separate debug and trace voltage domains.
VTREF
When using either the CoreSight 20 or Arm JTAG 20 connector, only one voltage domain is supported.
The voltage domain is determined using the VTREF signal.
DEBUG_VTREF
When using the Mictor adapter, or optional MIPI-34 or MIPI-60 adapters, the voltage domain of the
debug signals is determined using the DEBUG_VTREF signal.
TRACE_VTREF
When using the MIPI-60 cable, Mictor adapter, or optional MIPI-34 or MIPI-60 adapters, the voltage
domain of the trace signals is determined using the TRACE_VTREF signal.
If only the TRACE_VTREF signal is connected on a Mictor, MIPI-34, or MIPI-60 connector of a
target, the DSTREAM-ST unit uses that signal to determine the logic levels of both the debug and trace
signals.
Arm recommends connecting VTREF signals directly to one or more appropriate power rails on the
target board. If a series resistor is used for short-circuit protection, the value used must be less than
100Ω.
VTREF signals that are received by the DSTREAM-PT system are loaded with a resistance of
approximately 10K to ground. The signals are filtered, limited, and buffered to provide the required
VDD (Voh) and reference voltages (Vi(th)) for the I/O stages of the debug unit.
The DSTREAM-PT system supports debug and trace logic levels between 1.2V and 3.3V.
•
To be recognized by the DSTREAM-PT system as a valid target reference voltage, VTREF signals
must be above 800mV. VTREF signals above 800mV illuminate the VTREF LED on the Parallel
Trace probe.
•
Logic levels outside the 1.2V to 3.3V window might work, but are not guaranteed to work because
the DSTREAM-ST unit and Parallel Trace probe internally limit the VTREF signal to a minimum of
approximately 1.1V, and a maximum of approximately 3.4V.
The relationships of Voh and Vi(th) to VTREF are:
101714_0100_02_en
Note
Note
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1 Debug and trace interface
1.7 Target Voltage Reference (VTREF) signals
1-26
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