September
1998, Issue 98
TCP/IP
Networking
by
Ingo Cyliax
With
Ethernet chips becoming a dime a dozen, it’s
a lot easier to justify having your network Ethernet
driven. Ingo walks you through all the nitty-gritty
steps of how to get your Ethernet-based device working
with real-time capabilities.
When
I discussed network communication last month, I mentioned
that Ethernet is starting to be viewed as a device interface
bus. I also told you about the increasing availability
of Ethernet-based data-acquisition devices. This month,
let’s see what it takes to build a prototype of
an Ethernet-based device.
First
question: what do I define as an Ethernet-based device?
Basically, a device that has an Ethernet port as its
primary interface. A temperature sensor with an Ethernet
port is one example, but I’m not sure about the
economics of such a project.
To
make developing such a device more interesting to me,
it needs to solve one of my problems. So, here goes.
I
frequently use a prototyping system called a logic engine,
which is essentially a system tester. It has 128 I/O
ports and is controlled via a PC-compatible parallel
port.
The
protocol used over the parallel port needs nonstandard
software to drive it. This situation wasn’t a problem
when a DOS-based machine controlled this board. I simply
wrote a program to make the parallel port perform the
function I wanted.
With
the advent of Windows 95 and Windows NT–based systems,
controlling the parallel port becomes an issue. I now
need to write a device driver just so my program, which
wants to control the logic engine, can talk to it. What’s
worse, this device driver will probably break when I
try it with Win98 or when NTS comes out.
The
device I want to discuss is a Ethernet-to-parallel port
device that controls the logic engine. In a sense, the
parallel port–based logic engine becomes an Ethernet-based
logic engine.
This
technique has several advantages. First of all, I don’t
need to write and install a device driver on the system
controlling the logic engine. Secondly, I can share
the logic engine between workstations or over the Internet.
Finally,
I can use a variety of programming languages on many
platforms to talk to this device. All my language on
the workstation needs now is a network library. I don’t
have to write various libraries like I did for the old
parallel-based interface.
But
before getting started on this project, I want to take
a look at one of its major components—TCP/IP.
