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CentOS 7.0 - man page for ieee1284_read_data (centos section 3)

IEEE1284_DATA(3)			    Functions				 IEEE1284_DATA(3)

NAME
       ieee1284_read_data, ieee1284_write_data, ieee1284_data_dir, ieee1284_wait_data - control
       the data lines

SYNOPSIS
       #include <ieee1284.h>

       int ieee1284_read_data(struct parport *port);

       void ieee1284_write_data(struct parport *port, unsigned char dt);

       int ieee1284_data_dir(struct parport *port, int reverse);

       int ieee1284_wait_data(struct parport *port, unsigned char mask, unsigned char val,
			      struct timeval *timeout);

DESCRIPTION
       These functions manipulate the data lines of the parallel port associated with port (which
       must have been claimed using ieee1284_claim(3)). The lines are represented by an 8-bit
       number (one line per bit) and a direction. The data lines are driven as a group; they may
       be all host-driven (forward direction) or not (reverse direction). When the peripheral is
       driving them the host must not.

       For ieee1284_data_dir the reverse parameter should be zero to turn the data line drivers
       on and non-zero to turn them off. Some port types may be unable to switch off the data
       line drivers.

       Setting the data lines may have side effects on some port types (for example, some Amiga
       ports pulse nStrobe).

       ieee1284_wait_data waits, up until the timeout, for the data bits specified in mask to
       have the corresponding values in val.

RETURN VALUE
       ieee1284_read_data returns the 8-bit number representing the data lines unless it is not
       possible to return such a value with this port type, in which case it returns an error
       code. Possible error codes:

       E1284_NOTAVAIL
	   Bi-directional data lines are not available on this system.

       E1284_INVALIDPORT
	   The port parameter is invalid (perhaps it has not been claimed, for instance).

       E1284_SYS
	   There was an error at the operating system level, and errno has been set accordingly.

       E1284_TIMEDOUT
	   The timeout has elapsed.

       Whereas ieee1284_read_data may return E1284_NOTAVAIL on its first invocation on the port,
       if it does not do so then it cannot until ieee1284_close is called for that port.

AUTHOR
       Tim Waugh <twaugh@redhat.com>
	   Author.

COPYRIGHT
       Copyright (C) 2001-2003 Tim Waugh

[FIXME: source] 			    06/17/2014				 IEEE1284_DATA(3)


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