Communications and Network, 2013, 5, 65-68
doi:10.4236/cn.2013.51B015 Published Online February 2013 (http://www.scirp.org/journal/cn)
Design and Implementation of Embedded Web Server
in Industrial Control Systems
Jianming Liu1, Yunjie Zhang2, Lili Xu3, Jincai Wang1
1Computer Department, Weifang Medical University, Weifang, China
2Electronic & Information Engineering Department, Tianjin Institute of Urban Construction, Tianjin, China
3Weifang Vocational College, Weifang, China
Received 2012
ABSTRACT
In the traditional project of ind ustry control, the field operator is the only man who watches productio n condition at the
production spot. Enterprise administers cannot obtain real-time production status and make real-time decision if they
don’t reach the production spot. Because of the development of Embedded Web Server such status is being changed.
The remote monitor and control mode based on Embedded Web Server provides complete exact real-time information
for managers, and makes it possible to make a decision in real time. In the paper, the design and implements of Embed-
ded Web Server are presented and the key realization technology of it is described in detail. EWS (Embedded Web
Server) will effectively lower system operating cost and improve maintaining efficiency, which has wide application
prospect and populari zat i o n v al ue in industrial control systems.
Keywords: Emb edd ed W eb Server (EWS); TCP/IP; HTTP; Industrial Control Systems
1. Introduction
With the rapid development of the computer and network
technology, it has caused the technical revolution with
the industrial control systems. Now, the network, open-
ing structure becomes the main developing trend of the
industrial control systems. At present, World-Wide Web
(WWW) is one of the most widely used internet applica-
tions. The technology is very rapidly penetrating many
social and business areas. Now most of embedded sys-
tems are still in use alone, so the embedded equipments
should be improved as soon as possible. On the other
hand, a huge amount of embedded equipments are based
on 8-bit microcontrollers, such as instrument and appa-
ratus, real- time application and process controlling,
home automation, etc. Without exception, the industrial
control systems can be equipped with Web servers for
providing Web-based network communication. This type
of Web server is called an Embedded Web Server (EWS).
Based on EWS, the remote monitor and control mode
provides complete exact real-time information for man-
agers, and makes it possible to make a decision in real
time [1].
In the conditions of EWS-equipped devices, the users
can use web browser to manage devices and to receive
and send data to browsers anywhere in the world in order
to configure, monitor and control them. By the Web
browsers, users can manage individual devices remotely.
This scheme provides a user with a simple but powerful
user interface. Most embedded devices based on 8-bit
microcontrollers, contain a small amount of memory, so
in the design and implementation of EWS, some optimi-
zation techniques must be applied. In this paper, a kind
of design and implementation of EWS has been intro-
duced and the key realization technology of it is de-
scribed in detail. The technology uses the 8-bit micro-
controllers and network interface controller, such as
UMC9005, RTL8019AS, CS8900, etc., and adopts thin
TCP/IP protocols to transmit data. The result of experi-
ment proves that it is feasible to realize the target at very
low costs [2].
2. System Architecture of the EWS
The architecture of whole system is shown in the Figure
1. A EWS is a web server that has been designed to em-
bed in different kinds of small devices. Anyone who is
authorized may access the system if he knows the IP of
the installed web server. The client doesn’t need install
any special software besides the internet Explorer or oth-
er browsers. By browser users who have been authorized
can configure, control the embedded device, and also set
up network of the web server.
A EWS communicates via thin HTTP to a Web
browser by receiving a request which indicates the op-
eration that the user wants to perform, and sends a re-

J. M. LIU ET AL.
66
sponse in the form of a Web page for viewing. The URL
determines what operation to perform, which is ex ecuted
by the embedded system application. Further, to incor-
porate living data into a response, the EWS must dy-
namically create the Web page to return to the Web
browser request. The living data is extracted from the
embedded system application by the EWS [3].
3. Hardware Implementation
This Hardware structure of EWS is mainly made up of
MCU, EEPROM, I/O interface and Ethernet communi-
cate controller and isolate wave filter, as Figure 2 shows.
In this system we adopt AT89S52 as MCU, 24c02 as
EEPROM, and RTL8019AS as network interface controller.
The Hardware structure of EWS is shown in Figure 2.
RTL8019AS is a high-integrated 10Mbps Ethernet
control chip produced by Realtek Company of Taiwan.
RTL8019AS has finished all functions based on MAC
layer of Ethernet protocol. AT24C02 is a 256B E2PROM,
which is used for keeping the configuration information
of EWS, for instance the IP address, MAC address, etc.
So in different environment, the parameter of the EWS
can be changed freely. In order to enhance the anti-in-
terference ability of the TCP/IP network, segregation
wave filter is used between RTL8019AS and RJ45 inter-
face. For different application, the I/O interface and the
device are added to the EWS [1].
For some system, 8051 MCU is not suitable to proc-
ess the task. Then the arm microprocessor is adopted
widely in the Industrial control systems. The design of
the EWS using S3C44B0X is show in Figure 3.
The embedded web server implementations usually
choose two kinds of methods: 1) Embedded processor
and network interface chip; 2) Embedded processor with
Ethernet interface. In the design of this paper, it adopts
the scheme 2. In the scheme, S3C44B0X processor and
RTL901AS network interface chip are chosen. Its con-
nection structure is as shown in Figure 3. RTL901AS is
connected to S3C44B0X through the data bus and ad-
dress bus. Besides, interrupt of the RTL901AS is con-
nected to the NO 3, external interrupt the S3C44B0X.
4. Protocol Consideration
Web servers bring the desired HTML pages and pictures
over the world wide internet to the Web browser. At the
same time, TCP/IP communication happens. TCP/IP is
the standard protocol used in internet, which is too large
and too costly for most embedded applications. To make
it sense to have a web server in every device, the TCP/IP
stack used in device must be designed with reduced code
size for embedded applications. The TCP/IP that we re-
duced is called thin TCP/IP.
Embedded
device
Web
Browser Internet
HTTP
Server
THIN
TCP/ IP RTOS
Figure 1. The architecture of EWS.
MCU
(MCS51,
AVR, etc.)
Network
Controller
I/O interface
E
2
PROM
RJ45 Ethernet Filter
Figure 2. Hardware structure of EWS.

J. M. LIU ET AL. 67
Simplicity and versatility are a majo
e
/IP follows seven layers in OSI which is adopted
in work layer is the defi-
ni
control protocol provides a reliable
by
r concern when
dsigning thin TCP/IP. It is designed to be uncompli-
cated, straightforward, and flexible. Using a TCP/IP
connection, the web server is accessed over the internet
by a web browser to provide a graphical window into
embedded devices. The web server generates web pages
that are graphically displayed in the web browser. The
server and the browser communicate via the HTTP pro-
tocol.
TCP
to four layers (see Figure 4).
From the bottom of TCP/IP, net
tion type of physical network media. Such as Ethernet,
frame relay, ATM, and Token Ring. In internet layer
there are protocols: IP, ARP, IGMP, and ICMP. In EWS
we can only implement IP, ARP, and ICMP. IGMP does
not need to be implemented, because we assume that
routing process is conducted in routing table at local
server. For Diagnostic functions, ICMP can be added.
Then in Transport Layer there are two protocols, TCP
and UDP. We only implement TCP, because web servers
only need TCP. The implement of TCP protocol is
shown in Figure 5.
TCP transmission
te stream oriented service. The basic TCP task is di-
vided into 6 functional blocks, which includes tcpinput,
tcpprocess, tcpreceive, tcpwrite, tcpenqueue, and tcpout-
put. When the application wants to send TCP packets,
tcpwrite function is called. The tcpwrite received data
call tcpenqueue function, which is used to put the data
Figure 3. The design of the EWS using S3C44B0X.
Application Layer
T
Tr ra an ns sp po or rt t L La ay ye er r
I
In nt te er rn ne et t L La ay ye er r
N
Ne et tw wo or rk k I In nt te er rf fa ac ce e
Figure 5. The implement of TCP protocol.
into the appetwork
onnecti check
ess
l ad-
dr
re of TCP/IP, which is responsible for sending the
da
ropriate TCP data message if the n
on is ready. Tcp output function is used to c
it can send these data. For example, the receiving end
whether or not has adequacy receive buffer, and if condi-
tion is satisfied it then call th e iproute and ipoutput func-
tion.
Address conversion if referred to Top address mapped
to a physical address. ARP (Address Resolution Protocol)
is responsible for the address conversion. The ARP pro-
tocol working process is described as follows: when the
host generates an IP datagram, the datagram is sent to the
destination host. The 32bit the IP address should be
transformed into a 48bit Ethernet address, which is from
a logical Internet address to a corresponding physical
hardware.
The structure of the ARP Packets is as follows:
struct arp｛
unsigned int hardw；//hardware type
nd int ARPopcode：//ARP operation unsige
unsigned int prot；//protocol type
/har unsigned char hardwlen；/dware length
ar ocol length unsigned chprotlen；//prot
ha unsigned char target[5]；//target's addr
a[ oco unsigned char targetp3]；//target's prot
ess
unsigned char sendha[5]；//sender's address
unsigned char sendpa[3]；//sender's protocol ad-
dress
｝
In the network layer, the IP protocol is the basis and
the co
ta in the sequence of operations. For different network
between the host, such as TCP, UDP, ICMP and IGMP,
the IP datagram format is used for transmission. IP is
providing unreliable connectionless datagram transport
services. The IP protocol function, is consisted of the
Figure 4. TCP/IP protocol architecture layers.

J. M. LIU ET AL.
68
data to be transmitted combining with IP header proc-
essing, then packed IP datagram sending to the MAC
layer. At the same time, the IP layer receives datagrams
d char ipversionlen；//ip version &
he r iptypeser；//type of Service
d Int ipdatagramid；//datagram id
dress of
so na-
tio
to send HTML file. HTTP is a standard protocol
ustransferring documents between machines over
TC
from the lower layer (such as Ethernet device driver).
After header checksum and message processing, the re-
ceived datagrams are sent to the higher level -- TCP or
UDP layer.
The structure of the IP header is as following：
struct ipheadr｛
unsigne
ader length
unsigned cha
unsigned int ippacketlen；//total packet length
unsigne
unsigned Int ipfragmentoffset；//fragment offset
unsignedchar iptlmetollve；//tlm etollve
unsigned char ipprotocol；//ip protocol
unsigned Int ipchecksum；//header checksum
unsigned char ipsource[3]；//ip ad
urce
unsigned char ipdest[3]；//ip address of desti
n
｝；
The application layer of the TCP/IP is HTTP, which is
made
ed for
P/IP. HTTP is used to manipulate interconnected
documents around the globe. Each document is retrieved
from a web server operating on some computers with
access to the EWS. The document is used to refer to any
type of data, which can be text, graphics, sound or video.
Figure 6 shows the model of the HTTP process. As in
Figure 4, the most common HTTP client is the familiar
web browser [4]. The web browser issues an URL re-
quest to the web server in order to access a document.
The server must be operating before the browser initiates
its requested HTML pages. The server is the depository
for the web pages, and it handles requests and passes data
back to the browser. The browser does more difficult
work of presenting the text, displaying graphics, and
running j ava applets.
Figure 6. The model of HTTP process.
5. The Program Flow Diagram of the EWS
Next Figure 5 shows the program flow diagram of EWS.
After data pack is delivered to the RTL8019AS and
MCU through the RJ45 interface, the thin TCP/IP of
system carries on a data analyzed and a judgment of the
data flow direction, and wraps or unwraps data packets.
So the rest work will be going on con tinually. Ob viously,
the end processing result is dealt with by web Server [6].
In the flow chat of micro programs, a box represents
one micro instruction. If one operate should be per-
formed, the corresponding field will be set ‘1’, otherwise
k
EFERENCES
[4] G. J. Han, J. D. Wang, T. Lin and H. Zhao, “Design and
Realization ofer Based on Web
‘0’. When the micro instruction is sent to data path from
control memory, the corresponding module will wor
correctly. The machine instruction is interpreted and ex-
ecuted after the IR receives it. That is to say, it will exe-
cute the corresponding micro program segment. In ac-
cordance with the 3 higher bits (IR7-IR5), several
branches are produced. Each of the branches presents one
machine instruction . Finally, all of th e code s of th e micro
instructions are obtained.
6. Conclusions
The EWS is a good media to attach device to internet.
There are lots of benefits in app lying EWS technology to
industrial control systems field. The paper has presented
and the key realization technology of EWS. This system
is built with low cost and is easy to install. Many kinds of
microcontrollers (8 bit) can be adopted to realize the
system. In 21 century, termed Post-PC stage, it can be
imagined that the traditional sever will become lean sev-
er which can be operated without human intervention.
R
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