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Parallel port ABCs
Types of Parallel ports
Parallel port devices
Layout
Technical Support
PARALLEL PORT ABCs
DB25 connector with an 8 bit data bus (Pin 2-7) which is more popularly used for
computer printers while is still used for other devices.
The standard length of Printer Parallel cables is a maximum of 15 feet; although there
are 50 foot cables, it is not recommended that these cables be used as it can create poor
connection and data signals.
TYPES OF PARALLEL PORTS
Unidirectional - 4-bit standard port which by factory default did not
have the capability of transferring data both ways.
Bi-directional - 8-bit standard port which was released with the
introduction of the PS/2 port in 1987 by IBM and are still
found in computers today. The Bi-directional port is cable of sending 8-bits input and
output. Today, on multifunction printers, this port can be referred to as a
bi-directional, Centronics, PS/2 type or standard port.
EPP - The Enhanced Parallel Port (EPP) was developed in
1991 by Intel, Xircom and Zenith Data Systems and operates close to ISA bus speed and
can achieve transfer rates up to 1 to 2MB/sec of data.
EPP version 1.7 was released in 1992 and later adapted into the IEEE 1284 standard. All
additional features are adapted into the IEEE standard.
EPP version 1.9 never existed.
ECP - The Enhanced Capabilities Port (ECP), developed by Microsoft and Hewlett-Packard
and announced in 1992,
is an additional enhanced Parallel port. Unfortunately, with ECP, it
requires an additional DMA channel which can cause resource
conflicts.
PARALLEL PORT DEVICES
Printer - The most common use for the
Parallel port.
Scanner - Another
commonly used parallel device is the Parallel scanner. Parallel
scanners are a popular alternative to SCSI scanners because of how
easy they are to to install.
External Drives - Another popular use of the Parallel ports
are external drives such as the Iomega Zip Drive, which can be
easily removed from one computer and placed onto another.
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LAYOUT 
| PIN |
PURPOSE |
| Pin 1 |
-Strobe |
| Pin 2 |
+Data Bit 0 |
| Pin 3 |
+Data Bit 1 |
| Pin 4 |
+Data Bit 2 |
| Pin 5 |
+Data Bit 3 |
| Pin 6 |
+Data Bit 4 |
| Pin 7 |
+Data Bit 5 |
| Pin 8 |
+Data Bit 6 |
| Pin 9 |
+Data Bit 7 |
| Pin 10 |
-Acknowledge |
| Pin 11 |
+Busy |
| Pin 12 |
+Paper End |
| Pin 13 |
+Select |
| Pin 14 |
-Auto Feed |
| Pin 15 |
-Error |
| Pin 16 |
-Initialize Printer |
| Pin 17 |
-Select Input |
| Pin 18 |
-Data Bit 0 Return (GND) |
| Pin 19 |
-Data Bit 1 Return (GND) |
| Pin 20 |
-Data Bit 2 Return (GND) |
| Pin 21 |
-Data Bit 3 Return (GND) |
| Pin 22 |
-Data Bit 4 Return (GND) |
| Pin 23 |
-Data Bit 5 Return (GND) |
| Pin 24 |
-Data Bit 6 Return (GND) |
| Pin 25 |
-Data Bit 7 Return (GND) |
Below is an explanation of each of the above purposes.
Pin1 = Data acknowledgement when the signal is low.
Pin 2 - 9 = Data transfer pins.
Pin 10 = Acknowledge that the data has finished processing and when the
signal is high indicates ready for more.
Pin 11 = When the signal goes high indicate that the printer has accepted
the data and is processing it. Once this signal goes low and Pin 10 goes high will accept
additional data.
Pin 12 = Printer paper jam when signal is high or no signal if printer
jam.
Pin 13 = When high signal printer is indicating that it is on-line and
ready to print.
Pin 14 = When low signal PC has indicated that the printer inset a line
feed after each line.
Pin 15 = Printer sends data to the computer telling it that an error has
occurred.
Pin 16 = When low signal PC has requested that the printer initiate an
internal reset.
Pin 17 = When low signal the PC has selected the printer and should in
return prepare for data being sent.
Pin 18 - 25 = Ground.
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CH000271