PARPORT.TXT- By KG.


Parallel Ports
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A parallel port has eight lines for sending all the bints for one
byte of data simultaneously across eight wires. This interface is
fast and usually is reserved for printers rather than
computer-to-computer communications. The only problem with
parallel ports is that cables cannot be extended for any great
length without amplifying the signal, or else errors will occur
in the signal.

The parallel port of the PC, XT and AT is unidirectional. Data
travels only one way from the computer to the port, to the parallel
device. On the PS/2, the parallel port is bidirectional so that
data can travel to or from the port.

Most applications do not use the bidirectional capability of the
PS/2 parallel ports.


Programming The Parallel Port In QBasic
-----------------------------------------
This will help you understand how to program the parallel port
directly using a programming language like QBasic. You may
use another language as long as you understand how to program
the port.
Below is a quick list of access numbers for each pin...
 Pin   Access Number
 2     1
 3     2
 4     4
 5     8
 6     16
 7     32
 8     64
 9     128
To turn on one of these pins you simply...
 OUT port, accessnumber
Where port is the number of the parallel port, for LPT1 (first
parallel port) the number would be 888 (378 hex).
To turn on more then one pin you add the values together, for
example lets say you want to turn on pins 4 and 7 and 8 you simply...
 OUT port, 4 + 32 + 64
To turn off all the pins you simply...
 OUT port, 0


Standard 25-Pin Parallel-Port Connector Pinout
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Pin     Description                Direction
1       -Strobe                    Out
2       +Data bit 0                Out
3       +Data bit 1                Out
4       +Data bit 2                Out
5       +Data bit 3                Out
6       +Data bit 4                Out
7       +Data bit 5                Out
8       +Data bit 6                Out
9       +Data bit 7                Out
10      -Acknowledge               In
11      +Busy                      In
12      +Paper End                 In
13      +Select                    In
14      -Auto Feed                 Out
15      -Error                     In
16      -Initialize printer        Out
17      -Select Input              Out
18-25   -Data Bit Returns (ground)