procedure bios_rs232_init(comport: integer; comparm: word);
  procedure async_close(drop_dtr: boolean);
  procedure async_clear_errors;
  procedure async_reset_port(
    comport  : integer;
    baudrate : word;
    parity   : char;
    wordsize : integer;
    stopbits : integer
  );
  function  async_open(
    comport  : integer;
    baudrate : word;
    parity   : char;
    wordsize : integer;
    stopbits : integer
  ): boolean;
  procedure async_send(c: char);
  function async_receive(var c: char): boolean;
  procedure async_receive_with_timeout(secs: integer; var c: integer);
  procedure async_stuff(ch: char);
  procedure async_find_delay(var one_ms_delay: integer);
  procedure async_init(
    async_buffer_max : integer;
    async_obuffer_max: integer;
    async_high_lev1  : integer;
    async_high_lev2  : integer;
    async_low_lev    : integer
  );
  function  async_carrier_detect: boolean;
  function  async_carrier_drop: boolean;
  procedure async_term_ready(ready_status: boolean);
  function  async_buffer_check: boolean;
  function  async_line_error(var error_flags: byte): boolean;
  function  async_ring_detect: boolean;
  procedure async_send_break;
  procedure async_send_string(s: string);
  procedure async_send_string_with_delays(
    s          : string;
    char_delay : integer;
    eos_delay  : integer
  );
  function  async_percentage_used: real;
  procedure async_purge_buffer;
  function  async_peek(nchars: integer): char;
  procedure async_setup_port(
    comport      : integer;
    base_address : integer;
    irq_line     : integer;
    int_numb     : integer
  );
  procedure async_release_buffers;
  procedure async_flush_output_buffer;
  procedure async_drain_output_buffer(max_wait_time: integer);
  function  async_port_address_given(com_port: integer): boolean;
  procedure async_send_now(c: char);
  function  async_wait_for_quiet(
    max_wait: longint; wait_time: longint
  ): boolean;
  { --- }
  procedure send_modem_command(modem_text: string);
  function  set_params(first_time: boolean): boolean;
  procedure initialize_modem;