1. Sequential Statements
Module F3.2

2. Sequential Statements
Statements executed sequentially within a process
If Statements
Case Statements
Loop Statements
While Loops
For Loops

3. Sequential Statements (cont.)
Exit Statement
Next Statement
Null Statement
Variable Assignment Statement
Signal Assignment Statement
Procedure Call Statement
Return Statement

4. Sequential Statements (cont.)
Wait Statement
Assertion Statement
Report Statement

5. If Statement [[ if_label:]] if boolean_expression then
{{ sequential_statement }}
{{ elsif boolean_expression then
{{ sequential_statement }} }}
[[ else
{{ sequential_statement }} ]]
end if [[ if_label ]] ;

6. Synthesis of 2-to-1 Mux using IF-ELSE Statement

7. Case Statement [[ case_label:]] case expression is
(( when choices => {{ sequential_statement }}))
{{ o o o }}
end case [[case_label]] ;
choices <= (( simple_expression ||
discrete_range || others ))
{{ | o o o }}

8. Synthesis of 4-to-1 Mux using CASE Statement

9. Null Statement [[label:]] null; No action is taken.
Can be used when a sequential statement is required.
For example,
in a case statement.
as a stub before we write the code for a process.

10. Loop Statement [[loop_label:]] loop {{ sequential_statement }}
end loop [[loop_label:]] ;
An infinite loop

11. Exit Statement [[label:]] exit [[loop_label]]
[[when boolean_expression]] ;
loop …
exit when condition;
...
end loop;
… -- jump here when condition is true ;

12. Next Statement [[label:]] next [[loop_label]]
Starts a new iteration of a loop.
[[label:]] next [[loop_label]]
[[when boolean_expression]] ;
loop …
next when condition;
...
end loop;

13. Next Statement loop statement-1; next when condition; statement-2;
end loop;
loop
statement-1;
if not condition then
statement-2;
end if;
end loop;

14. While Loop [[loop_label:]] while condition loop
{{ sequential_statement }}
end loop [[loop_label:]] ;

15. For Loop [[loop_label:]] for identifier in discrete_range loop
{{ sequential_statement }}
end loop [[loop_label:]] ;
discrete_range <=
type_mark [[ range simple_expression
(( to || downto )) simple_expression ]]
|| simple_expression (( to || downto ))
simple_expression

16. For Loop
The identifier is a loop parameter that is implicitly declared.
process is
variable a,b: integer;
begin
a := 10;
for a in 0 to 7 loop
b := a;
end loop;
-- a = 10 and b = 7
...
end process;

17. For Loop A for loop body will not execute for a null range
for i in 10 to 1 loop
...
end loop;
Loop will exit
immediately
for i in 10 downto 1 loop
...
end loop;
i takes on values 10, 9, 8, 7, 6, 5, 4, 3, 2, 1

18. Example of FOR loop