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bioscom
=======

Syntax
------

     #include <bios.h>
     
     int bioscom(int cmd, char data, int port);

Description
-----------

This function accesses the BIOS interrupt 0x14 function, serial
communication services.  The valid values of cmd are:

0 - initialize com port (DATA is the settings)
1 - write byte to port
2 - read byte from port
3 - get port status

For initialization, the byte is made up of the following bits:

     0000 0000
     7654 3210  Meaning
     
     ---- --10  7 bits/character
     ---- --11  8 bits/character
     ---- -0--  1 stop bit
     ---- -1--  2 stop bits
     ---X 0---  no parity
     ---0 1---  odd parity
     ---1 1---  even parity
     000- ----  110 baud
     001- ----  150 baud
     010- ----  300 baud
     011- ----  600 baud
     100- ----  1200 baud
     101- ----  2400 baud
     110- ----  4800 baud
     111- ----  9600 baud

Return Value
------------

The return value is a sequence of bits that indicate the port status
and, for cmd=0 and 3, the modem status.  For read/write operations, the
lower eight bits are the character read.

     1111 1100 0000 0000
     5432 1098 7654 3210  Meaning
     
     ---- ---- ---- ---1  CTS change
     ---- ---- ---- --1-  DSR change
     ---- ---- ---- -1--  ring change
     ---- ---- ---- 1---  carrier detect change
     ---- ---- ---1 ----  CTS present
     ---- ---- --1- ----  DSR present
     ---- ---- -1-- ----  ring present
     ---- ---- 1--- ----  carrier detect
     ---- ---1 ---- ----  data ready
     ---- --1- ---- ----  overrun error
     ---- -1-- ---- ----  parity error
     ---- 1--- ---- ----  framing error
     ---1 ---- ---- ----  break detected
     --1- ---- ---- ----  transmit holding register empty
     -1-- ---- ---- ----  transmit shift register empty
     1--- ---- ---- ----  time out (=1 if error present for cmd=1,2)

Example
-------

     bioscom(0, 0xe3); /* 9600 baud, no parity, one stop, 8 bits */
     for (i=0; buf[i]; i++)
       bioscom(1, buf[i]);