Specifications

SLAA137A
MSP430 Internet Connectivity 7
2.6 Hypertext Transfer Protocol
The hypertext transfer protocol (HTTP) is an application level protocol. It is a generic, stateless,
object oriented protocol that can be used for many tasks, such as name servers and distributed
object management systems, through extension of its request methods (commands). It uses a
client-server relationship and is based on a stream-oriented transport layer, such as TCP.
Today, the most important use is transferring HTML documents with multimedia contents
between Internet servers and clients (WWW). It works with the principle of request and
response. The simplest case is that a client establishes a connection to a server and requests a
content referred by a uniform resource identifier (URI) that specifies the path and name of the
resource. Commonly, this is done by navigating with the web browser. These URIs are
structured like a file path. After decoding the request, the server starts transferring the resource
to the client. The requests (also called methods) are sent as simple ASCII strings with a trailing
carriage return (CR) and line feed (LF) (Table 2).
Table 2. Important HTTP Methods
Method Description
GET A client requests a resource from a server. Afterwards, the server sends a header field and the
resource to the client.
HEAD Similar to get, but only the header-information about the resource is sent, not the resource itself.
POST Used to transfer information from client to server (for example, pushing a button on a web page).
The response from a server contains some header lines. Each one has a CR and LF at its end.
An additional CR and LF at the end of the last line of the header indicate that the data is
following. In most cases, this will be an HTML page or a picture file. After transferring the
content, the connection is usually closed again. HTTP protocol version 1.0 is described in RFC
1945.
3 Hardware Description
The two main components of the demonstration board are the MSP430F149 microcontroller
from Texas Instruments and the CS8900A ethernet controller from Crystal™ Semiconductor
Corporation.
The MSP430F149 used in the demonstration board has 60KB of flash memory and 2KB of
RAM. This makes it a good choice for storing and transferring web pages. It has also six
general-purpose input/output ports that can be used not only for interfacing to the LAN
controller, but also to realize a user project.
The CS8900A is a low-cost ethernet LAN controller optimized for industrial-standard-architecture
(ISA) personal computers. The features that made it very suitable for this project are its highly
integrated design, which reduces the amount and cost of external components, and its very
easy-to-handle bus interface. Most LAN controllers that are on the market have a PCI bus
interface. The CS8900A bus interface is simple to interface with a microcontroller directly.
General I/O port pins of the MSP430 are used to provide a bus interface to the LAN controller.
The availability of this device in a 3-V version is another benefit for interfacing it with the
MSP430.