Freescale Semiconductor MCF51QE128RM manual Automatic Compare Function, MCU Wait Mode Operation

Analog-to-Digital Converter (S08ADC12V1)

example, in 10-bit mode, with the bus clock selected as the input clock source, the input clock divide-by-1 ratio selected, and a bus frequency of 8 MHz, then the conversion time for a single conversion is:

	23 ADCK Cyc	+	5 bus Cyc
Conversion time =				= 3.5 ms
	8 MHz/1		8 MHz

Number of bus cycles = 3.5 ms x 8 MHz = 28 cycles

NOTE

The ADCK frequency must be between fADCK minimum and fADCK maximum to meet ADC specifications.

11.4.5Automatic Compare Function

The compare function can be configured to check for an upper or lower limit. After the input is sampled and converted, the result is added to the two’s complement of the compare value (ADCCVH and ADCCVL). When comparing to an upper limit (ACFGT = 1), if the result is greater-than or equal-to the compare value, COCO is set. When comparing to a lower limit (ACFGT = 0), if the result is less than the compare value, COCO is set. The value generated by the addition of the conversion result and the two’s complement of the compare value is transferred to ADCRH and ADCRL.

Upon completion of a conversion while the compare function is enabled, if the compare condition is not true, COCO is not set and no data is transferred to the result registers. An ADC interrupt is generated upon the setting of COCO if the ADC interrupt is enabled (AIEN = 1).

NOTE

The compare function can monitor the voltage on a channel while the MCU is in wait or stop3 mode. The ADC interrupt wakes the MCU when the compare condition is met.

11.4.6MCU Wait Mode Operation

Wait mode is a lower power-consumption standby mode from which recovery is fast because the clock sources remain active. If a conversion is in progress when the MCU enters wait mode, it continues until completion. Conversions can be initiated while the MCU is in wait mode by means of the hardware trigger or if continuous conversions are enabled.

The bus clock, bus clock divided by two, and ADACK are available as conversion clock sources while in wait mode. The use of ALTCLK as the conversion clock source in wait is dependent on the definition of ALTCLK for this MCU. Consult the module introduction for information on ALTCLK specific to this MCU.

A conversion complete event sets the COCO and generates an ADC interrupt to wake the MCU from wait mode if the ADC interrupt is enabled (AIEN = 1).

MCF51QE128 MCU Series Reference Manual, Rev. 3

Freescale Semiconductor 233

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