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ANALOGINPUTANALOGOUTPUT
Bill Giovino
22-Sep-2000
While today’s browsers can perform a myriad of tasks, the core task is receiving the
data in an HTTP protocol packet and rendering the data, via appropriate formatting,
in the browser area so that it can be read and understood by the user.
While Figure 1 appears to apply to a conventional World Wide Web server & PC
client, the exact same model and description can apply to an Embedded Internet
model:
      Embedded Web Server (EWS)                  Figure 2                                    Client
In Figure 2 the client/server model is the same as in Figure 1; the Web Server in this
case is a processor, usually a microcontroller, with an embedded TCP/IP stack and a
physical interface to a TCP/IP network. The Embedded Web Server also contains
the web pages, stored in Flash or EEPROM, that are transferred over the TCP/IP
connection to a destination browser.
For simplicity’s sake these examples show only one client and one server, but of
course the TCP/IP networks that they are connected to can have multiple clients
and servers on the same network.
Embedded Internet Explained
A microcontroller with an embedded TCP/IP stack (called an “Embedded Web
Server”, or EWS) sends pages over a physical layer connection (ex: DSL, Cable, or
more commonly Ethernet) to a remote computer with a browser. The computer with
the browser could be in the same room or on the opposite side of the globe. The
browser reads the HTML formatting and displays a page in the browser window. The
user can send data to the EWS stack thru a form on the page, in the exact same way
one fills out a form on the World Wide Web – data is entered or buttons selected and
then the user presses the “Submit” button.
Once “Submit” is pressed, the form data is sent over the physical connection and is
received by the TCP/IP stack in the remote microcontroller. The EWS’s stack then
passes the submitted data to user code in program memory in exactly the same way
that parameters are passed to a subroutine. The EWS’s application code then takes
over and can activate a motor or request a reading from an I/O pin.
TCP/IP
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