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Using Parallel Ports
Parallel ports,
commonly used by printers, transmit data in parallel, 8 bits at a time. If
the data is transmitted in parallel over a very long cable, the integrity
of the data is sometimes lost because bits may separate from the byte they
belong to. Most parallel cables are only 6 feet long, though no
established standards sets maximum cable length. However, avoid using a
parallel cable longer than 15 feet to ensure data integrity.
Hewlett-Packard recommends the cables be no longer than 10 feet.
Parallel ports were
originally used only for printers. However, some parallel ports are now
used for input devices. These bi-directional parallel ports are often used
for fast transmission of data over short distances. One common use is to
download and upload data from a PC to a laptop. Some external CD-ROM
drives use a bi-directional parallel port to transmit and receive data. If
you use an existing parallel port to install a peripheral device,
installation is very simple. Just plug the device into the port and load
the software. To accommodate a second parallel port, configure the port as
LPT2.
Types of Parallel
Ports
Parallel ports fall
into three categories: standard, enhanced parallel port (EPP), and
extended capabilities port (ECP). The standard parallel port (SPP) is
sometimes called a normal parallel port or a Centronics port, named after
the 36- pin Centronics connection used by printers (see the figure below).
A standard port only allows data to flow in one direction and is the
slowest of the three types of parallel ports.
EPP and ECP are both
bi-directional. ECP was designed to increase speed over EPP by using a DMA
channel; therefore, when using ECP mode you are using a DMA channel. Over
the years, both hardware and software manufacturers have implemented
several parallel port designs, attempting to increase speed and
performance.
To help establish
industry standards, a committee was formed in the early 90s supported by
the Institute of Electrical and Electronics Engineers (IEEE), which
created the IEEE 1284 standards for
parallel ports. These standards require backward compatibility with
previous parallel port technology. Both EPP and ECP are covered under the
IEEE 1284 specifications.
Connecting Serial
And Parallel Ports
Follow these steps to
connect serial ports to the systemboard, as shown in the figure below:
1. Look for the edge
color on the cables to orient the cables to pin 1 on the systemboard
connection.
2. Connect the two
cables to the COM 1 and COM 2 connections on the systemboard.
3. Remove a plate cover
from the back of the case and mount the port adapter in the empty slot,
using the screw from the cover to secure the adapter. The parallel port
adapter is connected in a similar way.
Pin Parallel Port
Pin Connections
1 Output Strobe
2 Output Data bit 0
3 Output Data bit 1
4 Output Data bit 2
5 Output Data bit 3
6 Output Data bit 4
7 Output Data bit 5
8 Output Data bit 6
9 Output Data bit 7
10 Input Acknowledge
11 Input Busy
12 Input Out of
paper
13 Input Select
14 Output Auto feed
15 Input Printer
error
16 Output Initialize
printer
17 Output Select
input
18 Input Ground for
bit 0
19 Input Ground for
bit 1
20 Input Ground for
bit 2
21 Input Ground for
bit 3
22 Input Ground for
bit 4
23 Input Ground for
bit 5
24 Input Ground for
bit 6
25 Input Ground for
bit 7
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