modelsim 里的always语句中只能用reg不能用wire 那我应该怎么写

In Verilog, `wire` is used to represent a signal that can be read but not written, while `reg` is used to represent a signal that can be both read and written. In a `always` block, the statements inside it describe how the signals should be updated in response to certain events, such as a clock edge.

In ModelSim, you can use `wire` and `reg` in an `always` block, but there are some important differences to keep in mind.

If you want to use a signal inside an `always` block as both read and write, you should declare it as a `reg`. If you want to use a signal inside an `always` block as read-only, you can declare it as a `wire`.

Here is an example:

reg signal_reg;

wire signal_wire;

always @(posedge clk) begin
  signal_reg <= some_expression;
  // signal_wire cannot be written to here
  // use signal_reg instead if you need to update the value of the signal
  if (signal_wire) begin
    // do something
  end
end

In this example, `signal_reg` is a `reg` and can be both read and written inside the `always` block. `signal_wire` is a `wire` and can only be read, not written. If you need to update the value of `signal_wire`, you should update its source outside of the `always` block.