Monday, August 11, 2008

VHDL Part 8 : integer vs natural vs positive

I am fond of using generic statements since this makes the codes I am writing more flexible. I mean I can use them as components in different topblocks without editing them. I will just have to map their generics to my main block's generics.

VHDL allows a user to define his own data types.

Integer is a data type that covers integer values from -2147483647 to +2147483647.

A subtype is a type with limits. Operations between different data types are not allowed but operations with a subtype and its respective data type is allowed.

Natural is a subtype that limits the range from 0 to +2147483647.
Positive is a subtype that covers 1 to 2147483647.

I often use natural and positive in my generic statements.

(1) Pedroni, V., Circuit Design with VHDL, The MIT Press, 2004.
(2) Pellerin, D. and Taylor, D., VHDL Made Easy, Prentice Hall PTR, 1996.


Tausen said...

Thanks for clearing this up, much appreciated.

Vivek Joshi said...

Thanks a ton