Thomas.Betker@xxxxxxxxxxxxxxxxx schrieb am 30.06.2015 um 12:56: > Hello Hartmut: > >>> The scaling factor for VREFP is 3.0/4096, not 1.0/4096; fix this to > get >>> correct readings. >> >> I just had a look at the datasheet [1], table 3-1 on page 37, and >> get the feeling >> that this scaling factor also applies to the VREFN channel. What is >> your opinion? >> >> [1] http://www.xilinx.com/support/documentation/user_guides/ >> ug480_7Series_XADC.pdf > > The table provides the following references: > - VREFP: Figure 2-10, transfer function 3*unsigned(code)/4096 > - VREFN: Figure 2-3, transfer function 1*unsigned(code)/4096 > > The table also says about VREFN: "The supply sensor is also used to > measure VREFN, thus 1 LSB = 3V/4096." I agree that this is not consistent > (by Figure 2-3, 1 LSB = 1V/4096), but I didn't have the means to check > which version is true as VREFN is close to 0V either way. > > The situation is simpler for VREFP as UG480 is unambiguous here, and by > measuring the actual voltage we can tell 1.25V and 0.41V easily apart, > even when taking some measurement errors into account. In other words, we > have to use the factor 3 to get correct results for VREFP (thus the > patch), while either factor returns plausible results for VREFN. > > I would suggest opening a webcase with Xilinx for clarification, and > adding another patch for VREFN if the factor 3 is confirmed. Can you do > this? If not, I can take care of it, but it may take a while as I am > pretty busy at the moment. > Go ahead, whenever you find the time. I don't have a Xilinx device, just reviewing the IIO patches and got a bit curious when reading through the data sheet. > Best regards, > Thomas > -- > To unsubscribe from this list: send the line "unsubscribe linux-iio" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
