# Scale and Offset Analog Output RT Box

**URL:** https://forum.plexim.com/t/scale-and-offset-analog-output-rt-box/3070
**Category:** RT Box
**Created:** [May 15, 2026, 12:45am UTC](https://forum.plexim.com/t/scale-and-offset-analog-output-rt-box/3070 "2026-05-15T00:45:24Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![rizalsaputra](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/rizalsaputra/32/2747_2.png) [@rizalsaputra](https://forum.plexim.com/u/rizalsaputra)
#### Post date: [May 15, 2026, 12:45am UTC](https://forum.plexim.com/t/scale-and-offset-analog-output-rt-box/3070/1 "2026-05-15T00:45:25Z")

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Hello,  
I am currently configuring the scale and offset settings for the Analog Out in my open-loop GFM model (SPI). When running the offline simulation, I receive the following warning: _“An output is less than the selected Coder Target Analog output voltage lower limit (0 V).”_ After investigating the issue, I found that the RT Box output, particularly the Vpcc signal during transient conditions, reaches approximately -0.55 V. The warning disappears when I change the Analog output voltage range in the Coder/Target settings to -5 V to 5 V or -10 V to 10 V.

However, I would like to ask whether it is safe for the STM32 ADC input if I keep the current Analog Output scale and offset configuration while using an Analog output voltage range of -5 V to 5 V. Can the STM32 ADC accept negative input voltages?

 ![image](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/a/a825eeab6d581a026ea7ab97535fdb85e0f91ec9.png)

[Open\_Loop\_GFM\_SPI.plecs](https://dub1.discourse-cdn.com/flex006/404) (191.6 KB)

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### Author: ![Bryan\_Lieblick](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/bryan_lieblick/32/10_2.png) [@Bryan\_Lieblick](https://forum.plexim.com/u/Bryan_Lieblick)
#### Post date: [May 15, 2026, 3:55pm UTC](https://forum.plexim.com/t/scale-and-offset-analog-output-rt-box/3070/2 "2026-05-15T15:55:10Z")

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> Can the STM32 ADC accept negative input voltages?

No - see the Section 5.2 of the [STM32 G474 Datasheet](https://www.st.com/resource/en/datasheet/stm32g474cb.pdf). All pins should not go -0.3V below Vss (basically ground) otherwise there may be “permanent damage to the device”.

Note if you are using the [LaunchPad-Nucleo interface board](https://www.plexim.com/products/rt_box/launchpad_interface) then there are built-in protections against this. From the **Analog Output** section:

> Furthermore, to safeguard the MCU inputs from overvoltage, each analog output channel is  
> clamped to 0 V and 3.3 V with two Schottky diodes

 ![image](https://europe1.discourse-cdn.com/flex006/uploads/plecs/original/2X/5/5dd20b378545b195dd4235b923171659b0b9bb8b.png)

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<div class="post-metadata">

### Author: ![rizalsaputra](https://dub1.discourse-cdn.com/flex006/user_avatar/forum.plexim.com/rizalsaputra/32/2747_2.png) [@rizalsaputra](https://forum.plexim.com/u/rizalsaputra)
#### Post date: [May 16, 2026, 1:24pm UTC](https://forum.plexim.com/t/scale-and-offset-analog-output-rt-box/3070/3 "2026-05-16T13:24:17Z")

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Mr @Bryan_Lieblick thankyou for your response. It was very helpful to me.