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94 lines
2.4 KiB
94 lines
2.4 KiB
6 years ago
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# DAC - analog output
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The DAC unit has two analog outputs and can either output a DC level, or one of the pre-defined waveforms. Those waveforms are generated using a DDS principle, the numerical equivalent of a PLL.
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- DC
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- SINE
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- TRIANGLE
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- SAWTOOTH UP
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- SAWTOOTH DOWN
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- RECTANGLE
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The DDS output speed is limited by the processor speed; properly shaped waveforms can
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be generated up to tens of kHz, obviously a better resolution is achieved with slower waveforms.
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DDS provides a very precise frequency adjustment at the expense of jitter. Faster frequencies tend to became more "pixelated" as there are fewer counter steps per period.
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The ADC unit further supports dithering using a noise generator and a sawtooth wave,
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provided by the STM32's hardware. Those are used e.g. to increase ADC resolution by introducing artificial noise through a large resistor.
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## Commands
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### WAVE_DC (0)
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Set a DC level, disable DDS for the channel
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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- u16 - level 0-4095
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### WAVE_SINE (1)
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Start a DDS sine waveform
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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### WAVE_TRIANGLE (2)
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Start a symmetrical triangle waveform
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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### WAVE_SAWTOOTH_UP (3)
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Start a rising sawtooth
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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### WAVE_SAWTOOTH_DOWN (4)
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Start a falling sawtooth
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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### WAVE_RECTANGLE (5)
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Start a rectangle waveform (pulse train)
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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- u16 - ontime in DDS table length (presently 0-8191)
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- u16 - high level 0-4095
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- u16 - low level 0-4095
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### SYNC (10)
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Synchronize the two channels (set phase = 0)
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### SET_FREQUENCY (20)
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Set the frequency
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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- float32 - frequency (Hz)
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### SET_PHASE (21)
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Set a channel's phase, relative to the initial synchronized phase.
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It's recommended to set phase only of one channel, leaving the other at 0°.
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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- u16 - phase in DDS table length (presently 0-8191)
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### SET_DITHER (22)
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Set dithering mode and strength
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*Request:*
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- u8 - channels (1-first, 2-second, 3-both)
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- u8 - noise type (0-none, 1-white, 2-triangle)
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- u8 - number of noise bits
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Please note that setting high number of noise bits can lead to overflow/underflow
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(probably a STM32 bug).
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## Events
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*No events defined for this unit type.*
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