I m a beginner in verilog please help in this regard which i m mentioning below

[aahieo]

I want to check a byte whether it has an "x" bit.

How can i proceed for this

 

[h@ro]

can you clarify what you mean by " "x" bit"? If you mean checking whether a specific bit of a byte size register is some state "x" (1 or 0 ) simply use

if (reg_name[n] = x)

or to check if any bits in the byte are some state "x"

if ((reg_name[7] = x) | (reg_name[6] = x) ....etc)

There's many other ways it can be done, but that's the most obvious I can think of.

If you mean to check for the indeterminate state "x" which can be seen in some simulation software that is not 1 or 0, you won't find it. In terms of applying to hardware, registers initialise to 0, and even noise on a floating input pin is only ever seen as 1 or 0.

 

[dave_59]

If you are using a simulator that supports SystemVerilog, like ModelSim/Questa, you can use the expression

$isunknown(mybyte)

that returns 1'b1 if any bit in the expression is X or Z.

Otherwise you will have to use a reduction XOR operation

(^mybyte) === 1'bx

The three '=' identity operator is needed to compare to an 'x. The two '=' equality operator will always return false with an unknown.