@node bioscom, bios
@subheading Syntax

@example
#include <bios.h>

int bioscom(int cmd, char data, int port);
@end example

@subheading Description

This function accesses the BIOS interrupt 0x14 function, serial
communication services.  @code{port} should be the COM port (0=COM1,
1=COM2, etc).

The valid values of cmd are:

@table @asis
@item 0 - initialize com port (@var{data} is the settings)
@item 1 - write byte to port
@item 2 - read byte from port (@var{data} is ignored)
@item 3 - get port status
@item
@end table

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

@example
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
@end example

For writing a character out to the port, the return value's lower
8 bits contain the same byte as passed as the @var{data} argument.

For reading a character from the port, the value of @var{data} is
ignored, and the lower 8 bits of the return value contain the byte
read.  Also, the "timeout" bit in the upper 8 bits is used as an error
indicator in this case (0=success, 1=error).  If it indicates an
error, you should call the "get port status" variant to get the
detailed error bits.

@subheading 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.

@example
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)
@end example

@subheading Portability

@portability !ansi, !posix

@subheading Example

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