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104 lignes
2.8 KiB
104 lignes
2.8 KiB
\section{DAC Unit}
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The digital/analog unit works with the two-channel \gls{DAC} hardware peripheral. It can be used in two modes: \gls{DC} output, and waveform generation.
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The waveform mode implements direct digital synthesis (explained in \cref{sec:theory_dac_dds}) of a sine, rectangle, sawtooth or triangle wave. The generated frequency can be set with a sub-hertz precision up to the lower tens of kHz. The two outputs can use a different waveform shape, can be synchronized, and their phase offset and frequency are dynamically adjustable.
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\subsection{DAC Configuration}
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\begin{inicode}
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[DAC:dac@13]
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# Enabled channels (1:A4, 2:A5)
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ch1_enable=Y
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ch2_enable=Y
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# Enable output buffer
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ch1_buff=Y
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ch2_buff=Y
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# Superimposed noise type (NONE,WHITE,TRIANGLE) and nbr. of bits (1-12)
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ch1_noise=NONE
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ch1_noise-level=3
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ch2_noise=NONE
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ch2_noise-level=3
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\end{inicode}
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\subsection{DAC Commands}
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Channels are specified in all commands as a bit map:
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\begin{itemize}[nosep]
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\item 0x01 -- channel 1
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\item 0x02 -- channel 2
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\item 0x03 -- both channels affected at once
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\end{itemize}
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\begin{cmdlist}
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0 & \cname{WAVE\_DC}
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Set a \gls{DC} level, disable \gls{DDS} for the channel
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& \begin{cmdreq}
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\cfield{u8} channels
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\cfield{u16} level (0--4095)
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\end{cmdreq} \\
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1 & \cname{WAVE\_SINE}
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Start a sine waveform
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& \begin{cmdreq}
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\cfield{u8} channels
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\end{cmdreq} \\
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2 & \cname{WAVE\_TRIANGLE}
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Start a symmetrical triangle waveform
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& \begin{cmdreq}
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\cfield{u8} channels
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\end{cmdreq} \\
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3 & \cname{WAVE\_SAWTOOTH\_UP}
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Start a rising sawtooth waveform
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& \begin{cmdreq}
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\cfield{u8} channels
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\end{cmdreq} \\
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4 & \cname{WAVE\_SAWTOOTH\_DOWN}
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Start a dalling sawtooth waveform
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& \begin{cmdreq}
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\cfield{u8} channels
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\end{cmdreq} \\
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5 & \cname{WAVE\_RECTANGLE}
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Start a rectangle waveform
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& \begin{cmdreq}
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\cfield{u8} channels
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\cfield{u16} on-time (0--8191)
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\cfield{u16} high level (0--4095)
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\cfield{u16} low level (0--4095)
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\end{cmdreq} \\
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10 & \cname{SYNC}
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Synchronize the two channels. The phase accumulator is reset to zero.
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& \\
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20 & \cname{SET\_FREQUENCY}
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Set the channel frequency
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& \begin{cmdreq}
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\cfield{u8} channels
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\cfield{float} frequency
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\end{cmdreq} \\
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21 & \cname{SET\_PHASE}
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Set a channel's phase. It is recommended to only set the phase of one channel, leaving the other at 0°.
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& \begin{cmdreq}
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\cfield{u8} channels
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\cfield{u16} phase (0--8191)
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\end{cmdreq} \\
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22 & \cname{SET\_DITHER}
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Control the dithering function of the \gls{DAC} block. A high noise amplitude can cause an overflow to the other end of the output range due to a bug in the \gls{DAC} peripheral. Use value 255 to leave the parameter unchanged.
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& \begin{cmdreq}
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\cfield{u8} channels
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\cfield{u8} noise type (0--none, 1--white, 2--triangle)
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\cfield{u8} number of noise bits (1--12)
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\end{cmdreq} \\
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\end{cmdlist}
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