Freescale Semiconductor MCF51QE128RM manual MCU Stop3 Mode Operation, MCU Stop2 Mode Operation

Analog-to-Digital Converter (S08ADC12V1)

11.4.7MCU Stop3 Mode Operation

Stop mode is a low power-consumption standby mode during which most or all clock sources on the MCU are disabled.

11.4.7.1Stop3 Mode With ADACK Disabled

If the asynchronous clock, ADACK, is not selected as the conversion clock, executing a stop instruction aborts the current conversion and places the ADC in its idle state. The contents of ADCRH and ADCRL are unaffected by stop3 mode. After exiting from stop3 mode, a software or hardware trigger is required to resume conversions.

11.4.7.2Stop3 Mode With ADACK Enabled

If ADACK is selected as the conversion clock, the ADC continues operation during stop3 mode. For guaranteed ADC operation, the MCU’s voltage regulator must remain active during stop3 mode. Consult the module introduction for configuration information for this MCU.

If a conversion is in progress when the MCU enters stop3 mode, it continues until completion. Conversions can be initiated while the MCU is in stop3 mode by means of the hardware trigger or if continuous conversions are enabled.

A conversion complete event sets the COCO and generates an ADC interrupt to wake the MCU from stop3 mode if the ADC interrupt is enabled (AIEN = 1).

NOTE

The ADC module can wake the system from low-power stop and cause the MCU to begin consuming run-level currents without generating a system level interrupt. To prevent this scenario, software should ensure the data transfer blocking mechanism (discussed in Section 11.4.4.2, “Completing Conversions) is cleared when entering stop3 and continuing ADC conversions.

11.4.8MCU Stop2 Mode Operation

The ADC module is automatically disabled when the MCU enters stop2 mode. All module registers contain their reset values following exit from stop2. Therefore, the module must be re-enabled and re-configured following exit from stop2.

11.5Initialization Information

This section gives an example that provides some basic direction on how to initialize and configure the ADC module. You can configure the module for 8-, 10-, or 12-bit resolution, single or continuous conversion, and a polled or interrupt approach, among many other options. Refer to Table 11-7, Table 11-8, and Table 11-9for information used in this example.

MCF51QE128 MCU Series Reference Manual, Rev. 3

234 Freescale Semiconductor

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