Relational operators in VHDL - Step-by-Step Execution

Concept Flow - Relational operators

Start

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Evaluate Left Operand

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Evaluate Right Operand

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Compare using relational operator

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Result: TRUE or FALSE

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Use result in condition or assignment

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End

Relational operators compare two values and return TRUE or FALSE based on the comparison result.

Execution Sample

VHDL

signal a, b : integer := 5;
signal result : boolean;

result <= (a < b);

This code compares if 'a' is less than 'b' and stores the boolean result.

Execution Table

Step	a	b	Expression	Evaluation	Result
1	5	5	a < b	5 < 5	FALSE
2	5	6	a < b	5 < 6	TRUE
3	7	6	a < b	7 < 6	FALSE
4	3	3	a = b	3 = 3	TRUE
5	4	5	a /= b	4 /= 5	TRUE
6	5	5	a /= b	5 /= 5	FALSE

💡 All comparisons evaluated; results are boolean TRUE or FALSE.

Variable Tracker

Variable	Start	After 1	After 2	After 3	After 4	After 5	After 6
a	5	5	5	7	3	4	5
b	5	5	6	6	3	5	5
result	N/A	FALSE	TRUE	FALSE	TRUE	TRUE	FALSE

Key Moments - 3 Insights

Why does '5 < 5' evaluate to FALSE?

Because relational operators check strict inequality; 5 is not less than 5, so the result is FALSE as shown in execution_table row 1.

What does the operator '/=' mean in VHDL?

It means 'not equal to'. For example, in execution_table rows 5 and 6, '4 /= 5' is TRUE and '5 /= 5' is FALSE.

Can relational operators be used with signals of type integer?

Yes, as shown in the sample code and execution_table, integers can be compared using relational operators.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of 'a < b' when a=7 and b=6?

A Undefined

B TRUE

C FALSE

D Error

💡 Hint

Check execution_table row 3 where a=7 and b=6.

At which step does 'a = b' evaluate to TRUE?

A Step 4

B Step 1

C Step 5

D Step 6

💡 Hint

Look at execution_table row 4 for the expression 'a = b'.

If 'a' changes from 4 to 5 at step 6, what is the result of 'a /= b'?

A TRUE

B FALSE

C Depends on previous steps

D Error

💡 Hint

See execution_table row 6 where a=5 and b=5.

Concept Snapshot

Relational operators in VHDL compare two values.
Common operators: <, <=, >, >=, =, /=.
They return boolean TRUE or FALSE.
Used in conditions and assignments.
Operands must be comparable types like integers.

Full Transcript

Relational operators in VHDL compare two values such as integers and return TRUE or FALSE. The operators include less than (<), less or equal (<=), greater than (>), greater or equal (>=), equal (=), and not equal (/=). For example, comparing if a < b evaluates to TRUE if a is less than b, otherwise FALSE. These operators are used in conditions and assignments to control logic flow. The execution table shows step-by-step how different values of 'a' and 'b' produce boolean results. Beginners often wonder why 5 < 5 is FALSE because it is not strictly less, and what '/=' means, which is 'not equal'. These operators work with signals of compatible types like integers. Understanding these basics helps in writing conditional logic in VHDL.