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Chapter 8 Analog-to-Digital Converter (ATD10B8CV3)
MC9S12XDP512 Data Sheet, Rev. 2.11
Freescale Semiconductor 371
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.
8.4.2.2 General Purpose Digital Input Port Operation
The input channel pins can be multiplexed between analog and digital data. As analog inputs, they are
multiplexed and sampled to supply signals to the A/D converter. As digital inputs, they supply external
input data that can be accessed through the digital port register PORTAD (input-only).
The analog/digital multiplex operation is performed in the input pads. The input pad is always connected
to the analog inputs of the ATD. The input pad signal is buffered to the digital port registers. This buffer
can be turned on or off with the ATDDIEN register. This is important so that the buffer does not draw
excess current when analog potentials are presented at its input.
Table 8-23. External Trigger Control Bits
ETRIGLE ETRIGP ETRIGE SCAN Description
X X 0 0 Ignores external trigger. Performs one
conversion sequence and stops.
X X 0 1 Ignores external trigger. Performs
continuous conversion sequences.
0 0 1 X Falling edge triggered. Performs one
conversion sequence per trigger.
0 1 1 X Rising edge triggered. Performs one
conversion sequence per trigger.
1 0 1 X Trigger active low. Performs
continuous conversions while trigger
is active.
1 1 1 X Trigger active high. Performs
continuous conversions while trigger
is active.