PC912XDP512F0MPVR datasheet(181/1348 Pages) FREESCALE

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Chapter 5 Analog-to-Digital Converter (S12ATD10B8CV2)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

181

5.4.2

Digital Sub-Block

This subsection explains some of the digital features in more detail. See register descriptions for all details.

5.4.2.1

External Trigger Input

The external trigger feature allows the user to synchronize ATD conversions to the external environment

events rather than relying on software to signal the ATD module when ATD conversions are to take place.

The external trigger signal (out of reset ATD channel 7, conﬁgurable in ATDCTL1) is programmable to

be edge or level sensitive with polarity control. Table 5-23 gives a brief description of the different

combinations of control bits and their effect on the external trigger function.

During a conversion, if additional active edges are detected the overrun error ﬂag ETORF is set.

In either level or edge triggered modes, the ﬁrst conversion begins when the trigger is received. In both

cases, the maximum latency time is one bus clock cycle plus any skew or delay introduced by the trigger

circuitry.

NOTE

The conversion results for the external trigger ATD channel 7 have no

meaning while external trigger mode is enabled.

Once ETRIGE is enabled, conversions cannot be started by a write to ATDCTL5, but rather must be

triggered externally.

If the level mode is active and the external trigger both de-asserts and re-asserts itself during a conversion

sequence, this does not constitute an overrun; therefore, the ﬂag is not set. If the trigger is left asserted in

level mode while a sequence is completing, another sequence will be triggered immediately.

Table 5-23. External Trigger Control Bits

ETRIGLE

ETRIGP

ETRIGE

SCAN

Description

Ignores external trigger. Performs one

conversion sequence and stops.

Ignores external trigger. Performs

continuous conversion sequences.

Falling edge triggered. Performs one

conversion sequence per trigger.

Rising edge triggered. Performs one

conversion sequence per trigger.

Trigger active low. Performs

continuous conversions while trigger

is active.

Trigger active high. Performs

continuous conversions while trigger

is active.

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