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 bioscom()               Communications I/O

 #include   <bios.h>

 int        bioscom(cmd,byte,port);
 int        cmd;                         Operation to perform
 char       byte;                        Bits to set communications port
 int        port;                        Specified I/O port

    Using BIOS interrupt 0x14, bioscom() carries out RS232
    communications, using the connection specified by 'port' (0 = COM1, 1
    = COM2, and so on).  'cmd' and 'byte' specify the type of action and
    the communications parameters.

    'cmd' can be one of the following:

           0    To set communications parameters to the value specified
                in 'byte'.
           1    To send the character in 'byte'.
           2    To receive a character.
           3    To get the current status of 'port'.

    'byte' is the result of "or"ing one value from each of these four
    groups. The bit settings represent the following:

                0x02     7 data bits
                0x03     8 data bits

                0x00     1 stop bit
                0x04     2 stop bits

                0x00     No parity
                0x08     Odd parity
                0x18     Even parity

                0x00     110 baud
                0x20     150 baud
                0x40     300 baud
                0x60     600 baud
                0x80     1200 baud
                0xA0     2400 baud
                0xC0     4800 baud
                0xE0     9600 baud

    Therefore, the value 0x9B in 'byte' (0x80 | 0x18 | 0x00 | 0x03) sets
    the communications port to 1200 baud, even parity, 1 stop bit, and 8
    data bits.

       Returns:     A 16-bit integer.

         Notes:     Regardless of the value of 'cmd', the upper 8 bits of
                    the return value are status bits:

                bit 15   Time out
                bit 14   Transmit shift register empty
                bit 13   Transmit holding register empty
                bit 12   Break detect
                bit 11   Framing error
                bit 10   Parity error
                bit 9    Overrun error
                bit 8    Data ready

                Depending on the value of 'cmd', the value of the lower 8
                bits of the return value varies:

                If 'cmd' is 1 (send a character) and bit 15 is set: The
                value in 'byte' could not be transmitted. If bit 15 is
                not set, the rest of the upper and lower bits are set
                appropriately.

                If 'cmd' is 2 (read a character) and none of the upper
                bits are set: The byte read is in the lower 8 bits of the
                return value.

                If 'cmd' is 0 or 3 (set parameters or return status): The
                upper bits are set as described.  The lower bits have the
                following meanings:

                bit 7    Received line signal detect
                bit 6    Ring indicator
                bit 5    Data set ready
                bit 4    Clear to send
                bit 3    Delta receive line signal detector
                bit 2    Trailing edge ring detector
                bit 1    Delta data set ready
                bit 0    Delta clear to send

   Portability:     IBM PC and compatibles only.

   -------------------------------- Example ---------------------------------

    The following statements set the RS232 port COM2 to 1200 baud, 8 data
    bits, 1 stop bit and even parity.  Next it attempts to receive a byte
    from COM2, and then send the value 0xAA on COM2.

           #include <stdio.h>      /* for 'printf' */
           #include <bios.h>       /* for 'bioscom' */

           #define PORT_COM2 1

           main()
           {
               int result;

               bioscom(0,0x80|0x18|0x00|0x03,PORT_COM2);   /* set COM2 *
               result = bioscom(2,0,PORT_COM2);            /* receive byte */
               printf("%x read from COM2, status bits = %x\n",
                       result & 0xFF,result & 0xFF00);
               result = bioscom(1,0xAA,PORT_COM2);         /* send 0xAA
           */  if (result & 0x8000)
                   printf("unable to send");
           }