Re: Access to parallel port in Linux and WinXP
From: Walter Roberson (roberson_at_ibd.nrc-cnrc.gc.ca)
Date: 10/20/04
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Date: 20 Oct 2004 01:00:22 GMT
In article <547d92f1.0410191321.29104ac6@posting.google.com>,
karan <karan@iitk.ac.in> wrote:
:Is it possible to make a program which can write to that parallel port
:buffer/register which stores the input data to the parallel port (from
:the printer). In effect, I am trying to manipulate the data registers
:of the parallel port.
That would probably depend on the exact chip used to impliment
the parallel port. Generally speaking, modern parallel ports are
designed to be bidirectional, so data written the I/O port would
not be read back when a read is done against the same port number,
with the chip looking at the read/write request to determine whether
to buffer in or out of the chip.
There isn't any reason why someone could not design the I/O registers
so that the reads had to be done to a different port number than was
used for the writes: it is more a convention than a requirement.
Looping back is not the normal mode of operation of a parallel port
chip, and designers often prefer to minimize the number of different
dataports needed rather than separate functionalities cleanly,
so the tendancy is to a single data port with a series of control
ports, and not to an input data port separate from the output data
port and separate from all of the control ports.
-- Reviewers should be required to produce a certain number of negative reviews - like police given quotas for handing out speeding tickets. -- The Audio Anarchist
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