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MC68HC908GR16 Datasheet, PDF (53/310 Pages) Motorola, Inc – Microcontrollers
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Freescale Semiconductor, Inc.
Analog-to-Digital Converter (ADC)
I/O Registers
3.7.2 ADC Analog Ground Pin (VSSAD)
The ADC analog portion uses VSSAD as its ground pin. Connect the VSSAD pin to
the same voltage potential as VSS.
NOTE: Route VSSAD cleanly to avoid any offset errors.
VSSAD and VREFL are double-bonded on the MC68HC908GR16.
3.7.3 ADC Voltage Reference High Pin (VREFH)
The ADC analog portion uses VREFH as its upper voltage reference pin. By default,
connect the VREFH pin to the same voltage potential as VDD. External filtering is
often necessary to ensure a clean VREFH for good results. Any noise present on
this pin will be reflected and possibly magnified in A/D conversion values.
NOTE:
For maximum noise immunity, route VREFH carefully and place bypass capacitors
as close as possible to the package. Routing VREFH close and parallel to VREFL
may improve common mode noise rejection.
VDDAD and VREFH are double-bonded on the MC68HC908GR16.
3.7.4 ADC Voltage Reference Low Pin (VREFL)
The ADC analog portion uses VREFL as its lower voltage reference pin. By default,
connect the VREFH pin to the same voltage potential as VSS. External filtering is
often necessary to ensure a clean VREFL for good results. Any noise present on this
pin will be reflected and possibly magnified in A/D conversion values.
NOTE:
For maximum noise immunity, route VREFL carefully and, if not connected to VSS,
place bypass capacitors as close as possible to the package. Routing VREFH close
and parallel to VREFL may improve common mode noise rejection.
VSSAD and VREFL are double-bonded on the MC68HC908GR16.
3.7.5 ADC Voltage In (VADIN)
VADIN is the input voltage signal from one of the eight ADC channels to the ADC
module.
3.8 I/O Registers
These I/O registers control and monitor ADC operation:
• ADC status and control register (ADSCR)
• ADC data register (ADRH and ADRL)
• ADC clock register (ADCLK)
MC68HC908GR16 — Rev. 1.0
MOTOROLA
Analog-to-Digital Converter (ADC)
For More Information On This Product,
Go to: www.freescale.com
Data Sheet
53
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