HCS08 datasheet(135/316 Pages) NXP

135 / 316 page

Analog-to-Digital Converter (S08ADCV1)

MC9S08SG8 MCU Series Data Sheet, Rev. 8

Freescale Semiconductor

135

are too fast, then the clock must be divided to the appropriate frequency. This divider is specified by the

ADIV bits and can be divide-by 1, 2, 4, or 8.

9.4.2

Input Select and Pin Control

The pin control registers (APCTL3, APCTL2, and APCTL1) are used to disable the I/O port control of the

pins used as analog inputs.When a pin control register bit is set, the following conditions are forced for the

associated MCU pin:

•

The output buffer is forced to its high impedance state.

•

The input buffer is disabled. A read of the I/O port returns a zero for any pin with its input buffer

disabled.

•

The pullup is disabled.

9.4.3

Hardware Trigger

The ADC module has a selectable asynchronous hardware conversion trigger, ADHWT, that is enabled

when the ADTRG bit is set. This source is not available on all MCUs. Consult the module introduction for

information on the ADHWT source specific to this MCU.

When ADHWT source is available and hardware trigger is enabled (ADTRG=1), a conversion is initiated

on the rising edge of ADHWT. If a conversion is in progress when a rising edge occurs, the rising edge is

ignored. In continuous convert configuration, only the initial rising edge to launch continuous conversions

is observed. The hardware trigger function operates in conjunction with any of the conversion modes and

configurations.

9.4.4

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 ADC module can be

configured for low power operation, long sample time, continuous conversion, and automatic compare of

the conversion result to a software determined compare value.

9.4.4.1

Initiating Conversions

A conversion is initiated:

•

Following a write to ADCSC1 (with ADCH bits not all 1s) if software triggered operation is

selected.

•

Following a hardware trigger (ADHWT) 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 ADCSC1 is

written and continue until aborted. In hardware triggered operation, continuous conversions begin after a

hardware trigger event and continue until aborted.

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