Freescale Semiconductor, Inc.
Pinout and Signal Descriptions
3.3 Power Supply Pins
Power and ground pins are described below and summarized in Table
3-1.
3.3.1 Internal Power (VDD) and Ground (VSS)
Power is supplied to the MCU through VDD and VSS. Because fast signal
transitions place high, short-duration current demands on the power
supply, use bypass capacitors with high-frequency characteristics and
place them as close to the MCU as possible. Bypass requirements
depend on how heavily the MCU pins are loaded.
3.3.2 External Power (VDDX) and Ground (VSSX
)
External power and ground for I/O drivers. Because fast signal
transitions place high, short-duration current demands on the power
supply, use bypass capacitors with high-frequency characteristics and
place them as close to the MCU as possible. Bypass requirements
depend on how heavily the MCU pins are loaded.
3.3.3 VDDA, VSSA
Provides operating voltage and ground for the analog-to-digital
converter. This allows the supply voltage to the ATD to be bypassed
independently. Connecting VDDA to VDD if the ATD modules are not
used will not result in an increase of power consumption.
3.3.4 Analog to Digital Reference Voltages (VRH, VRL)
VRH0, VRL0: reference voltage high and low for ATD converter 0.
VRH1, VRL1: reference voltage high and low for ATD converter 1.
If the ATD modules are not used, leaving VRH connected to VDD will not
result in an increase of power consumption.
Technical Data
MC68HC912DG128 — Rev 3.0
Pinout and Signal Descriptions
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