Why won't my DAC output a voltage larger than 2.56v?

[RWang.9]

Hi there,

I've been having difficulty trying to make the DAC channel 1 output 3.3v. The largest voltage that the DAC outputs is 2.56 volts which I measured with an oscilloscope. I try to set the output voltage to be higher with the following code snippet but the DAC doesn't output anything higher than 2.56 volts.

HAL_DAC_SetValue(&hdac, DAC_CHANNEL_1, DAC_ALIGN_12B_R, 4000);

I am using the stm32cube ide and there isn't many much I can configure for the DAC. I don't know if this is a configuration issue or a hardware issue.

[RWang.9]

The DAC output is connected to the PA4 pin and is set to analog.

Do you have any recommended content on GPIOA registers?

[RWang.9]

The DAC output is connected to the PA4 pin and the pin is in Analog mode.
Do you have any recommended content about GPIOA registers for me to read about?

[waclawek.jan]

Well, just check if MODER is 0b11 for this bit, and PUPDR is 0b00 (i.e. there's no pulldown switched on).

Looking at the Nucleo-64 schematics, there should be no load on board. You might try to measure resistance of given pin against ground, with powered-down board.

Try measuring using some other method - a multimeter perhaps?

JW

[RWang.9]

Do you know where I can check the MODER and PUPDR for the pin PA4 in stm32 cube ide? Also, if there's a syntax that could set the MODER and PUPDR could you tell me?

When I measured the resistance of unpowered board through the PA4 pin to the ground, it showed a resistance of 9ohms but I don't know if that contributes to a capped output voltage.

[waclawek.jan]

> When I measured the resistance of unpowered board through the PA4 pin to the ground, it showed a resistance of 9ohms

That's certainly unexpected. If there's nothing connected to PA4 on board or externally, it may be also a damaged pin on the mcu.

JW

PS.

> Do you know where I can check the MODER and PUPDR for the pin PA4 in stm32 cube ide?

I don't use the CubeIDE, but there should be a window with peripheral registers somewhere. Maybe go through the CubeIDE manual. I am talking about GPIOA_MODER and GPIOA_PUPDR.

[AScha.3]

Really 9 ohm ?​

Then remove the resistor or buy new board.

Here is useless to talk about.

[RWang.9 · Accepted solution]

Hi guys, I've solved the problem.

The issue was with the oscilloscope probe used to measure the DAC voltage. When I switched to using another probe, the oscilloscope measured the max voltage of the DAC to be 3.3V.