Cypress Semiconductor CY7C028V Manual de usuario descargar pdf (Pagina 5)

Middle-East J. Sci. Res., 19 (12): 1623-1629, 2014

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CMSIS Cortex Microcontoller Software Interface

Standard compliant

GSM and GPRS are developed for cellular mobile

communication. A GPRS connection with unlimited

duration of connectivity is charged only for the data

package transfers and adopted in several mobile remote

control/access systems. GPRS becomes a cost-effective

solution only if the data transfers can be optimized.

Once a GPRS connection has been established,

queried data can be relayed to the client via a central

server. Using a central server to relay the acquired data

has some disadvantages. First, a central server needs a

client interface framework. An additional data transfer

corresponds to time delays before the data are made

available to the client. In addition, since the server acts as

a relay, no direct bidirectional communication between

the client and the embedded system can be established. Fig. 2: Folder structure of tghe FTP server

This makes the system unsuitable for real-time control

applications. The basic idea behind real-time processing To directly access an embedded system, the IP

is that the embedded system is expected to respond to the address of the embedded device should be made available

queries in time. Real time should be fast enough in the to the client side. There are two choices available. A static

context in which the system is operating and reliable as (hard-coded) IP could be used, or the remote device

well. Real-time system correctness depends not only on should initiate a connection by reporting its IP. This

the correctness of the logical result of the computation choice is quite straightforward and simple. Although the

but also on the result delivery time. This method also usage cost remains unchanged, it requires a static IP

increases the data transfer cost as the number of clients setup by the service provider and involves monthly

increases due to the access amount of data transfers via recurring costs. The static IP is preferred for its simplicity

GPRS. in designing a system; however, its overhead may be

Direct communication, on the other hand, enables impractical. The other choice is to use a dynamic IP

access to only relevant information in the embedded assigned through a Dynamic Host Configuration Protocol

system by preprocessing the data. The embedded system (DHCP) server of the GSM provider for every connection

should also handle the web services. This eliminates the established. However, this IP needs to be known by any

need for a central server and reduces the amount of data client requesting an access to the embedded server. One

sent from the remote unit since only the queried data will solution is to broadcast this IP to a dummy FTP server

be transferred [12]. (where the bulky static information such as image data is

In the proposed system, the GPRS architecture also kept). The FTP server is a dummy server and does

and protocols are compliant with. This system is not require regular software updates or maintenance.

configured to be virtually online at all times in a GSM The folder structure of the FTP server is shown in Fig. 2.

network. An admin script is executed after the boot of the A script on the embedded device is configured to

operating system, initiating the GPRS connection software update its IP address on the FTP server in Hypertext

module. A PPP connection is established by a GPRS Meta-Language as an index.htm file, under a folder

modem that works at 900/1800/ 1900 MHz operating uniquely named by its hostname. This script simply

frequencies. A PPP daemon (PPPD) is used to manage the parses the current IP for that embedded device and sends

PPP network connections between the client and the an html file with the IP information of the embedded

embedded module. The PPPD is responsible for setting up device to the FTP server. Once this file is in place, a direct

the GPRS parameters, such as the connection speed and connection can be established with the desired embedded

compression. device by a simple query. An example embedded system,

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S. Philomina 1

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