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MC908QL4CDWE Datasheet(Hoja de datos) 46 Page - Freescale Semiconductor, Inc

No. de Pieza. MC908QL4CDWE
Descripción  M68HC08 Microcontrollers
Descarga  226 Pages
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Fabricante  FREESCALE [Freescale Semiconductor, Inc]
Página de inicio  http://www.freescale.com
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 46 page
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Analog-to-Digital Converter (ADC10) Module
MC68HC908QL4 Data Sheet, Rev. 8
46
Freescale Semiconductor
Whichever clock is selected, its frequency must fall within the acceptable frequency range for ADCK. If
the available clocks are too slow, the ADC10 will not perform according to specifications. If the available
clocks are too fast, then the clock must be divided to the appropriate frequency. This divider is specified
by the ADIV[1:0] bits and can be divide-by 1, 2, 4, or 8.
3.3.2 Input Select and Pin Control
Only one analog input may be used for conversion at any given time. The channel select bits in ADCSC
are used to select the input signal for conversion.
3.3.3 Conversion Control
Conversions can be performed in either 10-bit mode or 8-bit mode as determined by the MODE bits.
Conversions can be initiated by either a software or hardware trigger. In addition, the ADC10 module can
be configured for low power operation, long sample time, and continuous conversion.
3.3.3.1 Initiating Conversions
A conversion is initiated:
Following a write to ADCSC (with ADCH bits not all 1s) if software triggered operation is selected.
Following a hardware trigger event if hardware triggered operation is selected.
Following the transfer of the result to the data registers when continuous conversion is enabled.
If continuous conversions are enabled a new conversion is automatically initiated after the completion of
the current conversion. In software triggered operation, continuous conversions begin after ADCSC is
written and continue until aborted. In hardware triggered operation, continuous conversions begin after a
hardware trigger event and continue until aborted.
3.3.3.2 Completing Conversions
A conversion is completed when the result of the conversion is transferred into the data result registers,
ADRH and ADRL. This is indicated by the setting of the COCO bit. An interrupt is generated if AIEN is
high at the time that COCO is set.
A blocking mechanism prevents a new result from overwriting previous data in ADRH and ADRL if the
previous data is in the process of being read while in 10-bit mode (ADRH has been read but ADRL has
not). In this case the data transfer is blocked, COCO is not set, and the new result is lost. When a data
transfer is blocked, another conversion is initiated regardless of the state of ADCO (single or continuous
conversions enabled). If single conversions are enabled, this could result in several discarded
conversions and excess power consumption. To avoid this issue, the data registers must not be read after
initiating a single conversion until the conversion completes.
3.3.3.3 Aborting Conversions
Any conversion in progress will be aborted when:
A write to ADCSC occurs (the current conversion will be aborted and a new conversion will be
initiated, if ADCH are not all 1s).
A write to ADCLK occurs.
The MCU is reset.
The MCU enters stop mode with ACLK not enabled.




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