inp

read one byte from an 80x86 hardware port

Synopsis:

#include <conio.h>
unsigned int inp( int port );

Description:

The inp() function reads one byte from the 80x86 hardware port whose number is given by port.

A hardware port is used to communicate with a device. One, two or four bytes can be read and/or written from each port, depending on the hardware. Consult the technical documentation for your computer to determine the port numbers for a device and the expected usage of each port for a device.

When you use the inp() function, your program must be linked for privity level 1, and the process must be run by the superuser or a setuid program that's owned by the superuser but started by a regular user. For more information on privity, see

• the cc -T option
• the Linker PRIVILEGE option.

Returns:

the byte that was read

See also:

inpd(), inpw(), outp(), outpd(), outpw()

Examples:

#include <conio.h>

void main()
  {
    /* turn off speaker */
    outp( 0x61, inp( 0x61 ) & 0xFC );
  }

Classification:

Intel

Systems:

All (except DOS/PM)