Verilog Block statements

The block statements are a means of grouping statements together so that they act syntactically like a single statement. There are two types of blocks in the Verilog HDL:
— Sequential block, also called begin-end block
— Parallel block, also called fork-join block
The sequential block shall be delimited by the keywords begin and end. The procedural statements in
sequential block shall be executed sequentially in the given order.
The parallel block shall be delimited by the keywords fork and join. The procedural statements in parallel
block shall be executed concurrently.

1). Sequential blocks:

A sequential block shall have the following characteristics:
— Statements shall be executed in sequence, one after another.
— Delay values for each statement shall be treated relative to the simulation time of the execution of
the previous statement.
— Control shall pass out of the block after the last statement executes.
For example: —A sequential block enables the following two assignments to have a deterministic result:

begin
areg = breg;
creg = areg; // creg stores the value of breg
end

The first assignment is performed, and areg is updated before control passes to the second assignment.

2). Parallel blocks:

A parallel block shall have the following characteristics:
— Statements shall execute concurrently.
— Delay values for each statement shall be considered relative to the simulation time of entering the
block.
— Delay control can be used to provide time-ordering for assignments.
— Control shall pass out of the block when the last time-ordered statement executes.

The following example codes show parallel –

fork
#50 r = 'h35;
#100 r = 'hE2;
#150 r = 'h00;
#200 r = 'hF7;
#250 -> end_wave;
join

3). Block names:

Both sequential and parallel blocks can be named by adding : name_of_block after the keywords begin
or fork. The naming of blocks serves several purposes:

— It allows local variables, parameters, and named events to be declared for the block.
— It allows the block to be referenced in statements such as the disable statement

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