Difference between "logic" and "bit" data types.

Question

Hi all,  As we know "logic" data type has 4 states = 0, 1, X  &amp; Z, where as "bit" has only 2 states = 0 &amp; 1. Generally we can see use of "logic" as data type for all kind of signals on internet :rolleyes:. But I have read in book that for 2 states logic we can use "bit" as datatype.  So, my question is, 'can we use "bit" data type for those signals like clock or reset which have only 2 states  0 or 1 ?.' :confused: If no then why we can not use it, and if yes then what is advantage of using "bit" over "logic".   module test_example   (   input bit        clk                        ,        // system clock   input bit        reset_n   // system reset    );  In this is example I have use bit as datatype for clk and reset_n signal. because it is obvious that clock can not be X or Z. So there are many signals that will not be X or Z then why we used logic datatype for those instead of bit. I hope I am clear with my doubt. If anybody has answer for my question, please explain me. All answers are welcomed here..:)

altera_forum · Answer

Most people use logic when they could have used bit. The advantage of using logic is that you will see unknowns in simulation if something hasnt been given a value, or you get multiple drivers somewhere. With bit, errors may not be so obvious as X will not propogate and you'll only get a '0'.

But you are right, bit and reset should always be '1' or '0', so having them as bit wont really hurt.

altera_forum · Answer

--- Quote Start ---   As we know "logic" data type has 4 states = 0, 1, X  &amp; Z   --- Quote End ---    std_logic data type has 9 states: "U, X, 1, 0, Z, W, L, H, - " u: Uninitialized  x: Unknown 1: Logic 1 0: Logic 0 Z: High impendance W: Weak signal, can't tell if it should be 0 or 1 L: Weak signal that should probably go to 0 H: Weak signal that should probably go to 1 -: Don't care.    --- Quote Start ---   In this is example I have use bit as datatype for clk and reset_n signal. because it is obvious that clock can not be X or Z.   --- Quote End ---    In your example, U state can be useful if you forget to initialize a signal in your component testbench.

altera_forum · Answer

--- Quote Start ---  std_logic data type has 9 states: "U, X, 1, 0, Z, W, L, H, - " u: Uninitialized  x: Unknown 1: Logic 1 0: Logic 0 Z: High impendance W: Weak signal, can't tell if it should be 0 or 1 L: Weak signal that should probably go to 0 H: Weak signal that should probably go to 1 -: Don't care.    In your example, U state can be useful if you forget to initialize a signal in your component testbench.  --- Quote End ---    The OP is asking about Verilog. Std_logic is a VHDL concept.

altera_forum · Answer

thank you, Tricky for your reply.  And yes JRL this question is about Verilog  I am failed to mention that.

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Difference between "logic" and "bit" data types.

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