Bitselect
Formal Definition
The bitselect provides an access to individual bits of vectors.
Simplified Syntax
vector_identifier[expression];
Description
The bitselect can be used to access individual bits of vector net or
register data types. The bits can be addressed by using an
expression. If the expression value is out of bounds or it returns z
or x values, then the value returned by the reference is x. If one or
more bits of the address returned by the expression have an x or z
value, then the address expression is x.
The bitselect can be applied to any net vectors, regs,
integers,
and time register data
types. The bitselection of a register declared as real
or realtime is illegal.
Examples
Example 1
reg [3:0] vect;
vect = 4'b0001;
If the value of address expression is 0 then returned value is 1
(vect[0] = 1).
If the value of address expression is 3 then returned value is 0
(vect[3] = 0).
If the value of address expression is 4 then returned value is x
(vect[4] = x).
If the value of address expression is x or z then returned value is x
(vect[1'bx] = x).
Example 2
reg [0:3] vect;
vect = 4'b0001;
If the value of address expression is 3 then returned value is 1
(vect[3] = 1).
If the value of address expression is 0 then returned value is 0
(vect[0] = 0).
Example 3
reg [7:0] vect;
vect = 4;
Fills vect with the pattern 00000100 (MSB is bit 7, LSB is bit 0).
Important Notes

If the address expression is out of bounds or it returns an x or z
value, then the returned value is x.

The bitselect of real or realtime registers is illegal.
