[SAMC] DAC clock source and speed

[Simon]

I'm looking at the DAC on the SAMC series of microcontrollers. I have not come across any clock speed requirements for the DAC. I also do not know how long it takes for a conversion to happen in clock cycles.

[MK14]

From  https://ww1.microchip.com/downloads/aemDocuments/documents/MCU32/ProductDocuments/DataSheets/SAM-C20-C21-Family-Data-Sheet-DS60001479J.pdf

When you search for  '  GCLK_DAC  ', it seems to say:

The voltage pump uses the asynchronous GCLK_DAC clock, and requires that the clock frequency be at least four
times higher than the sampling period.

Which since it seems to be 350kHz, max DAC (sampling/update) data rate. 4 x 0.350 = 1.4 MHz minimum, and the maximum is stated as 48 MHz.

MAX is given as:

fGCLK_DAC DAC input clock frequency 48 MHz

10-bit, 350 ksps Digital-to-Analog Converter (DAC) in the SAM C21

Which (at a somewhat quick look at the datasheet), is a fixed rate, independent of other settings, unless you disable/stop it, e.g. for power saving (sleep/idle) reasons.

But I'M NOT 100% sure about that (i.e. fixed at 350 kHz, while running).

They seem to prefer/intend for you to use its interrupt or DMA, to use it, in a time controlled manner. But I suppose you could still use it manually in the software.

[Simon]

Ah, good detective work, I thought the DAC would be covered in the analogue section of electrical specs completely.

So there is still no clue as to the actual clock cycles required to carry out a conversion other than maybe the dropping of a hint in the voltage pump settings. I don't need speed but have so far just run everything off the one clock channel at 48MHz

[ataradov]

Conversion time is variable and depends on the previous value. You can clock the DAC with 48 MHz, there is no issue doing that. If you need specific sampling rate, you must use external timing trigger, like a timer. And if you need regular updates at high rate, it is better to use DMA and trigger DMA transfers from the timer.

[MK14]

More information about the DAC, seems to be here:

https://microchipdeveloper.com/32arm:samd21-dac-overview

Conversion Time
DAC conversion time is approximately 2.85 μs. You must ensure that new data is not written to the DAC before the last conversion is complete. Conversions should be triggered by a periodic event from a Timer/Counter or another peripheral.

Also, this one (about driving software and stuff):
http://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-42110-SAM0-Digital-to-Analog-(DAC)-Driver_Application%20Note_AT03244.pdf

[Simon]

Conversion time is variable and depends on the previous value. You can clock the DAC with 48 MHz, there is no issue doing that. If you need specific sampling rate, you must use external timing trigger, like a timer. And if you need regular updates at high rate, it is better to use DMA and trigger DMA transfers from the timer.

No speed is not an issue, just avoiding more clocks than I need although there is little reason to have a 48MHz clock at all so could reduce it.