# HDL block diagram

Symbolator reads VHDL or Verilog component declarations and draws the block symbol: ports on the correct sides, buses grouped, names exactly as declared.

Generating it means the documentation cannot drift from the interface, which is the usual failure of hand-drawn block symbols.

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## When to reach for one

* Documenting module interfaces in a hardware design.
* Integration diagrams showing how modules connect.
* Design reviews where the port list is the subject.

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## How to draw it in Capable

| **Route**  | **Use when**                                            |
| ---------- | ------------------------------------------------------- |
| Symbolator | Generated directly from HDL source; never out of date.  |
| draw.io    | System-level diagrams built from the generated symbols. |

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## A worked example

A component declaration, drawn as a block symbol:

![HDL block diagram](https://help.gocapable.com/images/att1433960455.svg)

The source, which you can paste into a new diagram and edit:

```
component uart_rx is
  generic (
    CLK_FREQ  : integer := 50_000_000;
    BAUD_RATE : integer := 115_200
  );
  port (
    --# {{clocks|}}
    clk       : in  std_ulogic;
    rst_n     : in  std_ulogic;
    --# {{data|Serial}}
    rx        : in  std_ulogic;
    --# {{|Parallel}}
    data      : out std_ulogic_vector(7 downto 0);
    data_valid: out std_ulogic;
    frame_err : out std_ulogic
  );
end component;
```

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## A few things that catch people out

* Keep the source as the single definition; regenerate the diagram rather than editing it.
* Section comments group ports on the symbol, which is what makes a large interface readable.
* Generics belong on the symbol. They are part of the interface.

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## Related

[Memory layout diagramOffsets, widths and nested structures.](https://help.gocapable.com/diagrams/memory-layout-diagram.html)

[Neural network diagramLayers, connections and shapes.](https://help.gocapable.com/diagrams/neural-network-diagram.html)

[ExamplesWorking diagrams you can copy.](https://help.gocapable.com/diagrams/examples.html)

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_Approximately right is wrong here._