Assume there are two different modules (first_module
, second_module
). Both of the modules are synchronized with clock signal. first_module
has the following structure:
module first_module(
input clk,
input reset_n,
input in1,
output reg out1,
output reg out2
);
//******** some verilog codes *********
endmodule
And second_module
has similar structure:
module second_module(
input clk,
input reset_n,
input in1,
input in2,
output reg out1
);
//******** some verilog codes *********
endmodule
And then there is a module called top_module
which uses instances of both modules:
module top_module(
input clk,
input reset_n,
input insignal1,
input insignal2,
output outsignal1,
output outsignal2
);
first_module fm1(
.clk(clk),
.reset_n(reset_n),
.in1(insignal1),
.out1(outsignal1),
.out2(<connection1>) // to be connected to the connection2
);
second_module sm1(
.clk(clk),
.reset_n(reset_n),
.in1(insignal2),
.in2(<connection2>), // to be connected to the connection1
.out1(outsignal2)
);
endmodule
The aim is to connect connection1
to connection2
. According to my knowledge (if it is correct), we can either declare a single wire (let its name be connection
) and replace both <connection1>
and <connection2>
with it, or we can declare two distinct wires connection1
and connection2
, then:
assign connection2 = connection1;
And connect them accordingly.
Yes there is a difference. But not in your specific case.
Using a connection directly makes that is can be uni-directional or bi-directional depending on what the underlying ports in the module are.
But assign connection2 = connection1;
is only uni-directional.
Thus between bi-directional ports should use direct connections or you should only use bi-directional Verilog constructs between them. The assign ...
is not one of them.
But in you case the signal is uni-directional so it does not matter.
Note that modern FPGAs no longer have on-chip bi-directional buses. (At least I don't know one that has). Also in chip design on-chip buses are strongly discourage or outright forbidden by the manufacturers.
Therefore bi-directional signals are normally only present in the test-bench. As that does not get synthesized your question does not apply there.
Last but not least: In HDL design I would strongly discourage from changing the name of a signal for no apparent reason. Having the same name throughout the design makes it easier to debug and trace your signals post-synthesis.