You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
94 lines
2.4 KiB
94 lines
2.4 KiB
7 years ago
|
# DAC - analog output
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
- DC
|
||
|
|
- SINE
|
||
|
|
- TRIANGLE
|
||
|
|
- SAWTOOTH UP
|
||
|
|
- SAWTOOTH DOWN
|
||
|
|
- RECTANGLE
|
||
|
|
|
||
|
|
The DDS output speed is limited by the processor speed; properly shaped waveforms can
|
||
|
|
be generated up to tens of kHz, obviously a better resolution is achieved with slower waveforms.
|
||
|
|
|
||
|
|
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.
|
||
|
|
|
||
|
|
The ADC unit further supports dithering using a noise generator and a sawtooth wave,
|
||
|
|
provided by the STM32's hardware. Those are used e.g. to increase ADC resolution by introducing artificial noise through a large resistor.
|
||
|
|
|
||
|
|
## Commands
|
||
|
|
|
||
|
|
### WAVE_DC (0)
|
||
|
|
Set a DC level, disable DDS for the channel
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
- u16 - level 0-4095
|
||
|
|
|
||
|
|
### WAVE_SINE (1)
|
||
|
|
Start a DDS sine waveform
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
|
||
|
|
### WAVE_TRIANGLE (2)
|
||
|
|
Start a symmetrical triangle waveform
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
|
||
|
|
### WAVE_SAWTOOTH_UP (3)
|
||
|
|
Start a rising sawtooth
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
|
||
|
|
### WAVE_SAWTOOTH_DOWN (4)
|
||
|
|
Start a falling sawtooth
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
|
||
|
|
### WAVE_RECTANGLE (5)
|
||
|
|
Start a rectangle waveform (pulse train)
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
- u16 - ontime in DDS table length (presently 0-8191)
|
||
|
|
- u16 - high level 0-4095
|
||
|
|
- u16 - low level 0-4095
|
||
|
|
|
||
|
|
### SYNC (10)
|
||
|
|
Synchronize the two channels (set phase = 0)
|
||
|
|
|
||
|
|
### SET_FREQUENCY (20)
|
||
|
|
Set the frequency
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
- float32 - frequency (Hz)
|
||
|
|
|
||
|
|
### SET_PHASE (21)
|
||
|
|
Set a channel's phase, relative to the initial synchronized phase.
|
||
|
|
It's recommended to set phase only of one channel, leaving the other at 0°.
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
- u16 - phase in DDS table length (presently 0-8191)
|
||
|
|
|
||
|
|
### SET_DITHER (22)
|
||
|
|
Set dithering mode and strength
|
||
|
|
|
||
|
|
*Request:*
|
||
|
|
- u8 - channels (1-first, 2-second, 3-both)
|
||
|
|
- u8 - noise type (0-none, 1-white, 2-triangle)
|
||
|
|
- u8 - number of noise bits
|
||
|
|
|
||
|
|
Please note that setting high number of noise bits can lead to overflow/underflow
|
||
|
|
(probably a STM32 bug).
|
||
|
|
|
||
|
|
## Events
|
||
|
|
|
||
|
|
*No events defined for this unit type.*
|