MC908AP32CFBE Datasheet, PDF(254/324 Page) Freescale Semiconductor, Inc – The following revision history table summarizes changes contained in this document. For your convenience, the page number designators have been linked to the appropriate location.

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MC908AP32CFBE Datasheet, PDF (254/324 Pages) Freescale Semiconductor, Inc – The following revision history table summarizes changes contained in this document. For your convenience, the page number designators have been linked to the appropriate location.

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Analog-to-Digital Converter (ADC)

15.5.1 Wait Mode

The ADC continues normal operation in wait mode. Any enabled CPU interrupt request from the ADC can

bring the MCU out of wait mode. If the ADC is not required to bring the MCU out of wait mode, power

down the ADC by setting the ADCH[4:0] bits to logic 1âs before executing the WAIT instruction.

15.5.2 Stop Mode

The ADC module is inactive after the execution of a STOP instruction. Any pending conversion is aborted.

ADC conversions resume when the MCU exits stop mode. Allow one conversion cycle to stabilize the

analog circuitry before attempting a new ADC conversion after exiting stop mode.

15.6 I/O Signals

The ADC module has eight channels shared with port A I/O pins.

15.6.1 ADC Voltage In (VADIN)

VADIN is the input voltage signal from one of the eight ADC channels to the ADC module.

15.6.2 ADC Analog Power Pin (VDDA)

The ADC analog portion uses VDDA as its power pin. Connect the VDDA pin to the same voltage potential

as VDD. External filtering may be necessary to ensure clean VDDA for good results.

NOTE

Route VDDA carefully for maximum noise immunity and place bypass

capacitors as close as possible to the package.

15.6.3 ADC Analog Ground Pin (VSSA)

The ADC analog portion uses VSSA as its ground pin. Connect the VSSA pin to the same voltage potential

as VSS.

15.6.4 ADC Voltage Reference High Pin (VREFH)

VREFH is the power supply for setting the reference voltage VREFH. Connect the VREFH pin to the same

voltage potential as VDDA. There will be a finite current associated with VREFH (see Chapter 22 Electrical

Specifications).

NOTE

Route VREFH carefully for maximum noise immunity and place bypass

capacitors as close as possible to the package.

15.6.5 ADC Voltage Reference Low Pin (VREFL)

VREFL is the lower reference supply for the ADC. Connect the VREFL pin to the same voltage potential as

VSSA. There will be a finite current associated with VREFL (see Chapter 22 Electrical Specifications).

MC68HC908AP Family Data Sheet, Rev. 4

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Freescale Semiconductor

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