UART ReadString

When using UART to communicate, ReadString get an int parameter: what is its role ? Is it the number of lines, of chars ? Is there an example of use ?

If you mean ReadString in the DataReader class, the uint parameter is codeUnitCount as the Windows 10 API requires. However, a bug in all releases to date in our implementation is that it specifies how many bytes to read in the string, not the number of Unicode code points.