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2.2.4
Voltage Reference Low Select Header (W4)
Jumper header W4 selects the voltage reference low (VRL) source: either MPB
power (VSSA) or an external VRL source. The drawing below shows the factory
configuration: a fabricated jumper on pins 1 and 2. This configuration selects
VSSA as the VRL source.
To use an external VRL source, first place the fabricated jumper on W4 pins 2 and
3. Then connect the MCU VRL pin to the external VRL source. Each
configuration defines the best method for connecting the MCU VRL pin to the
external VRL source:
• MPB/MPFB – connect via the MPFB logic analyzer connector (refer to
Chapter 4 for the appropriate logic analyzer pin).
• MPB/MMDS1632 – connect via the VRL pin of the target MCU socket.
• MPB/Target System – connect via the VRL pin of the target system MAPI
bus.
Alternately, you may remove the jumper and wire-wrap directly to W4 pin 2.
Connecting directly to pin 2 is an option regardless of the configuration.
M68MPB16R3UM/D
HARDWARE PREPARATION AND INSTALLATION
W4
1
2
3
2-7
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