Sequential block(also known as procedure block)
key words: begin end
The sequential block executes a group of statements (blocking assignment statement) in a sequential manner in which they are specified.
Example:
reg x, y;
reg[1:0] z,w;
initial
begin
x = 1’b0;
y = 1’b1;
z = {x, y};
w = {y, x};
end
//exp2
reg x, y;
reg[1:0] z,w;
initial
begin
x = 1’b0;//done at time 0
#5 y = 1’b1;//done at time 5
#10 z = {x, y};//done at time 15
#20 w = {y, x};//done at time 35
end
Parallel block
Key word: fork join
The parallel block executes a group of statements concurrently as their execution starts at the same simulation time.
Example:
reg x,y;
reg [1:0] z,w;
initial
fork
x = 1b’0;//done at time 0
#5 y = 1b’1;//done at time 5
#10 z = {x, y};//done at time 10
#20 w = {y, x};//done at time 20
join
features of blocks
We can combine begin-end and fork-join blocks, name a block, and disable a block.
Example
initial
begin : block1// name a block
x = 1’b0;
fork : block2
#5 y = 1’b1;
#10 z = {x,y};
Join
#20 w = {y,x};
end
endmodule
We can use disable <block name> to stop executing a named block. It is like break in c, but c can only exit the current loop, disable can stop any named block in the design.
