Operation Principle; Reference Frequency; Adc Channel - L-Card L-502-P-G-D-I User Manual

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3.3. Operation principle

In the section 3.2 the concept of the L-502 project was summarized, where the main principles
of the module operation were listed. This section contains further details.

3.3.1. Reference frequency

f – a signal reference frequency, from which the conversion processes are synchronized to
ref
the ADC, DAC, digital input and digital output. The L-502 uses a common reference frequency that
synchronizes the start-up of the ADC, DAC, digital input and digital output to an accuracy of an
integer division of this frequency. In L-502, the reference frequency source can be internal (2.0 or
1.5 MHz) or external (with a frequency of not more than 2.0 MHz). In particular, the reference
frequency from the adjacent L-502 module can be used to form a synchronous multi-module
system.

3.3.2. ADC channel.

The analog data input channel is a channel with dynamic switching of up to 32 input physical
analog channels of the L-502 module to the input of a single internal ADC module. The process of
switching channels itself is hardware, according to a pre-configured control table. The input process
itself is conditionally divided into periodically alternating frame periods and interframe delay with
pre-configured durations of these periods (interframe delay, in particular, can be set to zero).
Duration of frame, interframe delay, ADC output sample timing - all these times can be configured,
but they are always a multiple of t
t = n / f – the ADC channel commutation period within the frame, equal to the sampling
sw sw ref
period of the ADC readouts, where n
The preset number of samples in the frame and the size of the control table n
1 to 256. In each cell of the control table, the physical number of the ADC polling channel is
prescribed. Within the frame, the control table will be read completely: from the 1st to the n
and the read sequence of physical channels will be used in the hardware control mechanism of the
channel switch.
The cell number of the control table is called the logical channel number. Accordingly,
logical channels can be up to 256, and physical - up to 32. For example, it gives the opportunity to
obtain a different frequency of polling different physical channels within the frame.
Frame time: t
k
If necessary, between intermittently following frames, a non-zero interframe delay t
duration n of synchronization frequency periods can be inserted:
d
t = n * t = n
d d ref
The frame period is equal to the sum of the frame length and the interframe delay:
t = t + t = n
ch k d
In other words, the frame period t
logical channel of the control table.
During interframe delay, the sample of control words does not advance, and the analog
channel switch is always set in accordance with the first cell of the control table.
Frequency of collection from one logical channel of the control table
f = 1/ t = f
ch ch ref
= 1/ f
ref
can be specified by an integer from 1 to 2097152
sw
= n к * t = n к * n
sw sw
/f , where n can be set with an integer from 0 to 2097151
d ref d
* n / f + n / f
к
sw ref d ref
/(n к * n + n ),
sw d
The device and principle of operation L-502.
- the period of the synchronization reference frequency.
ref
/ f
ref
is equal to the period of data collection from the same
ch
к can be set from
cell
th
with a
d