TC1784
Analog to Digital Converter (ADC)
User´s Manual
23-8
V1.1, 2011-05
ADC, V1.3
The functional characteristics of the request sources are adapted to the most common
application requirements. In all request sources, a continuous operation or a single-shot
operation can be selected. For continuous operation, the programmed sequence of
conversions requests are continuously issued (once started), whereas in single-shot
mode, each sequence of conversion requests has to be explicitly started. The trigger for
a conversion request or a sequence can be handled under SW control or can be
synchronized to ADC-external events, such as timer signals or port pins. For each
request source, the user can select an input signal (from 8 possible signals
REQTRx_[7:0]) as trigger input REQTRx and an input signal (from 8 possible signals
REQGTx_[7:0]) as gating input REQGTx.
•
Request source 0
(1-stage sequential source) can issue a conversion request for a
single input channel. The channel number can directly be programmed.
This mechanism could be used for SW-controlled conversion requests or HW-
triggered conversions of a single input channel. If programmed with a high priority, it
can interrupt the sequences of the other request sources to inject a single
conversion.
•
Request sources 1 and 3
(16-channel scan sources) can issue conversion requests
for a sequence of up to 16 input channels. It can be programmed which channel takes
part in this sequence. The sequence always starts with the highest enabled channel
number and continues towards lower channel numbers (order defined by the channel
number, each channel can be converted only once per sequence).
This mechanism could be used to scan input channels permanently or on a regular
time base. For example, if programmed with a low priority, some input channels can
be scanned in a background task to update information that is not time-critical.
•
Request sources 2 and 4
(4-stage sequential sources) can issue a conversion
request for a sequence of up to 4 input channels. The channel numbers can be freely
programmed, especially multiple conversions of the same channel within the
sequence are supported.
This mechanism could be used to support application-specific conversion sequences
that can not be covered by the scanning mechanism of request sources 1 or 3.
Especially for timing-critical sequences containing multiple conversions of the same
channel, one of these request sources should be used. For example, if programmed
with a medium priority, some input channels can be converted when a specified event
occurs (e.g. synchronized to a PWM) while the scan of other input channels of the
background task (handled by request source 1) is interrupted.
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