User`s guide

Ethernet Primer
Since an IT person may not be available, here is a quick explanation of Ethernet
communications and IP addressing and a few pointers at the end. Ethernet
communications can be complicated, especially in large corporations. If you do
not feel comfortable with this, you should contact an IT person. Assigning an
incorrect IP address may bump another individual off the network and is not a
good way to make friends.
Ethernet communications, as explained previously, is a serial communications
method, meaning bits of data are sent one after another and assembled to create
bytes of data. A bit is simply a one or a zero. A byte is a collection of 8 bits that
describe a number between 0 and 255. Often, a byte is used to describe a
character, a letter, number, symbol or code. So, for example, a capital A is
typically coded as 65. This code is called the ASCII code and you can see the
standard characters by searching for ASCII on the internet. Note that only the
numbers from 0 to 127 have standard meanings. The numbers above 127 are
used for a wide variety of things, often to generate non-english characters.
But we deviate from Ethernet… Ethernet is actually made of multiple layers. The
details of what these layers are is not so important. The important ones are the
hardware layer, the IP layer, and the TCP/UDP layer. The hardware layer is the
what it seems. Typically this is Ethernet cabling, switches and routers, but could
also be fiber optic cable, DSL lines, GPRS, etc. In general, you do not need to
worry about the hardware layer, except for proper cabling. Fortunately, there is
usually only two different types of cabling: direct and crossover. In most LAN’s
you will use exclusively direct cabling. This means that each pin on one side of
the cable corresponds to the same pin on the other side of the cable. In a
crossover cable, several pairs of pins are swapped. You would use a crossover
cable if you wanted to connect your PC directly to your Ethernet device (PLC, DAQ
device) without going through a switch, hub, or router. A switch or hub is simply
a traffic cop who allows Ethernet traffic to pass through to the appropriate spots.
Often switches/hubs are combined with your cable or DSL modem to allow
multiple computers to connect to the same internet connection.
On top of the hardware layer runs the IP layer. The IP layer handles the
addressing, thus the “IP Address”. The IP address is a collection of 4 numbers,
each between 0 and 255, separated by periods. These 4 numbers actually define
a single big number internally that ranges from 0 to a little over 4 billion, but
splitting that number into 4 sections makes it easier for us to read. A URL, such
as www.azeotech.com, is not an IP address. In fact, before your computer can
find azeotech.com it has to go to what is called a domain name server (DNS) to
find the IP address that corresponds to azeotech.com. Domain name servers are
typically provided by your ISP and their sole job is to take a URL and translate it
into the IP address. Ethernet cannot use URLs directly.
IP addresses are addresses and therefore every computer on the Internet has a
unique IP address. On the Internet, these addresses are distributed by a global
governing body, and typically provided to you by your ISP. Since IP addresses
basically define a number between 0 and about 4 billion, there can only be about