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Altera_Forum's avatar
Altera_Forum
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16 years ago

verilog module output to NULL

I created a complex module.

Not all output using all the time.

How can I redirect the unused outputs too "null".

sample:

uart_rx rx1 (.reset(uart_rst),

.rxclk(baud_clk),

.rx_read(rs),

.rx_data(data),

.rx_in(rx),

.rx_empty( to null),

.rx_busy(to null)

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    16 years ago

    Strictly speaking, if you don't want to use a port on a module, just don't connect it to anything. The synthesis tool is smart enough to remove any logic driving the ports.

    Examples: 

    uart_rx rx1 (
    .reset(uart_rst),
    .rxclk      (baud_clk   ),
    .rx_read    (rs         ),
    .rx_data    (data       ),
    .rx_in      (rx         ),
    .rx_empty   (           ),
    .rx_busy    (           )
);

    or 

    uart_rx rx1 (
    .reset(uart_rst),
    .rxclk      (baud_clk   ),
    .rx_read    (rs         ),
    .rx_data    (data       ),
    .rx_in      (rx         )  
);

    Alternatively, you can use a macro to get rid of it: 

    uart_rx rx1 (
    .reset(uart_rst),
    .rxclk      (baud_clk   ),
    .rx_read    (rs         ),
    .rx_data    (data       ),
    .rx_in      (rx         )
`ifndef USE_WORTHLESS_PORTS
    ,
    .rx_empty   (           ),
    .rx_busy    (           )
`endif
);

    And you can use synthesis directives if you don't want it in there for synthesis but do for simulation: 

    uart_rx rx1 (
    .reset(uart_rst),
    .rxclk      (baud_clk   ),
    .rx_read    (rs         ),
    .rx_data    (data       ),
    .rx_in      (rx         )
    // synthesis translate_off
    ,
    .rx_empty   (           ),
    .rx_busy    (           )
    // synthesis translate_on
);

    Jake
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    12 years ago

    If you leave output ports unconnected you will get warnings. depending of the number of unconnected ports the warnings may be annoying and most importantly may "hide" or obscure the real warnings you should be paying attention to.

    If you do not need an output, simple declare a dummy wire (or set of dummy wires) and connect the output to these.