VHDL – Description Models
VHDL • VHDL can be looked at as a model of a digital system – Powerful alternative to schematic based design • A change (transition) on the input may lead to a new system state and consequently a change of the output after a given time delay • Describes and simulates concurrent events IN OUT System/module Representation of a digital system
• The entity describes the interface to the outside world (connection pins of package) • The architecture describes the functionality of the circuit inside the entity (package)
Description models Structural Data-flow Behavioral
Description models Structural Data-flow Behavioral • Interconnection of components (black boxes) • Concurrent execution of statements • Can be used to create hierarchy in the code • Keywords: component & port map
Example of structural model
Example of structural model Can not directly connect together the input/output of a component to another component’s output/input! Must use an internal signal (such as int1 in this example), unless a connection to a port is made
entity declaration Component architecture declaration port component port A component is an entity that is used in another entity component port
Description models Structural Data-flow Behavioral • Non-procedural • Describes flow of data using concurrent statements – Concurrent execution of statements – Statement ”activated” by change on input • No correspondence between the order of elements / statements in the code
Code structure Concurrent statements area
Description models Structural Data-flow Behavioral • Procedural Describes circuit in terms of behaviour ( Algorithmic ) • High abstraction level (no details of actual HW implementation) • Keywords: process • Execution of a process is equivalent to a single concurrent statement. • All VHDL processes execute concurrently –
Code structure process: Concurrent a concurrent statements VHDL area statemen
Code structure process: Concurrent a concurrent statements VHDL area statemen
RTL – Register Transfer Level D Q D Q comb. comb. comb. clk logic clk logic logic Design abstraction which models a synchronous digital circuit in terms of the flow digital signals (data) between hardware registers, • And the logical operations performed on those signals •
Programmable logic block Combinational logic Logic block Boolean logic LUT A y B MUX C D q DFF clk Switch matrix Synchronous / Sequential logic
Recommend
More recommend