The bit type is predefined in the Standard package as an enumerated data type with only two allowable values: '0' and '1'.

Syntax:

type bit is ('0','1'); 

Description:

The bit type is the basic type to represent logical values. Note that there are only two values defined for the bit type and it is not possible to use it for high impedance and other non-trivial values such as Unknown, Resistive Weak, etc. (see Std_logic).

The default value of any object of the bit type is '0'.

Example:

signal A, B: bit; 
... 
A <= '1'; 
B <= not A;

Notes:

• Bit type values '0' and '1' are not identical to the Boolean values (false and true), respectively.
• Logical values for an object of the bit type must be written in quotes to distinguish them from Integer values.

See also:

Bit_Vector, Standard Package