Rule 10.1 violation with casting

[Frasew]

Hello,

my MISRA checker generates a MISRA violation 10.1 (The signedness of an integer type is converted implicitly.(signed -> unsigned)), although a casting is done.

My C code:

1: #include
2: typedef unsigned char U8;
...
w: U8 WriteProtect = (U8) true;
....
x: if(WriteProtect == (U8) false) {
....
y: WriteProtect = (U8) true;
....
z: }

The MISRA checker identifies line x and y as a rule 10.1 violation. Why is this a rule 10.1 violation although a casting is done? Interestingly the MISRA checker identifies line w as OK. Have anybody an idea what is my fault?

Is it generally impossible in MISRA to assign a signed var to an unsigned var?