You cannot handle negative voltages with the PSoC, they might even destroy it. (Except when using differential input, but even then the voltages cannot be below ground).
Apart from that: 0x000 corresponds to 0V, and negative voltages are represented as "two's complement" - a '-1' is then 0xFFFF. I think the ADC component data sheet explains that.
I am using delsig ADC, and I am using the differential input mode. My range is +/-6.2. So, can you explain why I can't use a negative voltage? I thought this what the differential input mode for!
The PSoC (all of them) specify in absolute maximum ratings the lowest and highest voltage that may be applied to any pin. This is GND to Vdd,
No negative voltages (less than GND) are allowed.
That's so confusing to me. In the attached picture, I got the shot from the Delsig datasheet, it says the Delsig can take negative voltage. I am not talking about pins, I am talking about the ADC_Delsig.
Also, it allows me to setup the range at +/- voltage as it appears on the second shot.
If the ADC_Delsig can't do negative, then what all these options in the second shot for?
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Differential mode means that you have two input signals. Both are measured, at the same time, and the ADC returns the difference between them. This difference can be negative or positive, depending on which signal is larger. But the input signals itself cannot be negative voltages, with reference to ground. Doing so will destroy your PSoC.