HCS08 datasheet(136/316 Pages) NXP

136 / 316 page

Analog-to-Digital Converter (S08ADCV1)

MC9S08SG8 MCU Series Data Sheet, Rev. 8

136

Freescale Semiconductor

9.4.4.2

Completing Conversions

A conversion is completed when the result of the conversion is transferred into the data result registers,

ADCRH and ADCRL. This is indicated by the setting of COCO. 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 ADCRH and ADCRL if

the previous data is in the process of being read while in 10-bit MODE (the ADCRH register has been read

but the ADCRL register has not). When blocking is active, the data transfer is blocked, COCO is not set,

and the new result is lost. In the case of single conversions with the compare function enabled and the

compare condition false, blocking has no effect and ADC operation is terminated. In all other cases of

operation, 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, the blocking mechanism 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.

9.4.4.3

Aborting Conversions

Any conversion in progress will be aborted when:

•

A write to ADCSC1 occurs (the current conversion will be aborted and a new conversion will be

initiated, if ADCH are not all 1s).

•

A write to ADCSC2, ADCCFG, ADCCVH, or ADCCVL occurs. This indicates a mode of

operation change has occurred and the current conversion is therefore invalid.

•

The MCU is reset.

•

The MCU enters stop mode with ADACK not enabled.

When a conversion is aborted, the contents of the data registers, ADCRH and ADCRL, are not altered but

continue to be the values transferred after the completion of the last successful conversion. In the case that

the conversion was aborted by a reset, ADCRH and ADCRL return to their reset states.

9.4.4.4

Power Control

The ADC module remains in its idle state until a conversion is initiated. If ADACK is selected as the

conversion clock source, the ADACK clock generator is also enabled.

Power consumption when active can be reduced by setting ADLPC. This results in a lower maximum

value for fADCK (see the electrical specifications).

9.4.4.5

Total Conversion Time

The total conversion time depends on the sample time (as determined by ADLSMP), the MCU bus

frequency, the conversion mode (8-bit or 10-bit), and the frequency of the conversion clock (fADCK). After

the module becomes active, sampling of the input begins. ADLSMP is used to select between short and

long sample times.When sampling is complete, the converter is isolated from the input channel and a

successive approximation algorithm is performed to determine the digital value of the analog signal. The

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