The concatenation is expressed by the brace characters {} bracketing two or more expressions separated by commas (Example 1). Concatenations can also be expressed using a repetition multiplier, which duplicates the expression it contains the number of times specified by the constant expression that precedes it (Example 2).

A concatenation expression can be either an identifier or a sized number. Unsized numbers are illegal because the size of all operands is required to calculate the size of an entire concatenation. A repetition multiplier should be a constant expression specified within the brace characters.

Examples

Example 1

reg [7:0] a;
{a, 4'b1110, b[2:1]}

Result of this expression has 14-bits ('a' has 8 bits, 4'b1110 has 4 bits, b[2:1] has 2 bits).

Example 2

{a, {2{b, c, d}}, a}

The above concatenation is equivalent to the following concatenation:

{a, b, c, d, b, c, d, a}

Important Notes

Repetition multiplier should be a constant expression.
Unsized numbers are illegal in concatenations (except as repetition multiplier).