ethernet using embedded systems

8/22/2019 Ethernet Using Embedded Systems

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ETHERNET USING EMBEDDED

SYSTEMS

PRESENTED BY

B.KOTI

REDDY

K.NARENDRA

REDDY

III ECE

LAKIREDDY BALIREDDY COLLEGE OF

ENGINEERNG

MYLAVARAM-521230


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ABSTRACT

Ethernet is a LAN Technology that is widely used in the networking field. It

is considered that Ethernet has two main drawbacks. The first one is that

transmitting host does not know whether the destination host is alive or not. The

second one is that the receiving host does not send acknowledgement to the

source informing that the data has been received. This makes the data

communication unreliable.

To overcome these two drawbacks, we go for Embedded Ethernet. It has

two ICs as its main components namely CrystalCS8900A and PIC16C74.

CrystalCS8900A IC has integrated memory to store packets temporarily while

PIC16C74 IC can be programmed to make decisions according to the

instructions of the host, to issue acknowledgements to the source, etc..,. This

paper explains how data communication using Embedded Ethernet takes place.


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ETHERNET

Ethernet is a popular L A N technology

A coaxial cable(Ether) carries signals at 10 Mbps

The connection between a computer and the cable requires a hardware

device called transceiver for sensing and sending signals.

A Host interface of Host adapter plugs into the computer bus and

connects to the transceiver.

Host interface controls the operation of transceiver according to

instructions of computer

Ethernet has a bus topology because all hosts share a single

communication channel

Costly of this assembly are replaced by an Embedded Ethernet board

which is a special high speed digital circuits

NEED FOR EMBEDDED ETHRNET

There are two main drawbacks in the existing Ethernet .They are

The transmitting host does not know whether the destination host is alive or not.

Acknowledgement is not issued by the receiving host to inform the source that the

data has been received.


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Hence the communication is supposed to be unreliable. To overcome these drawbacks,

Embedded Ethernet is used.

EMBEDDED ETHERNET

The Embedded Ethernet board consists of two ICs namely

1. Crystal CS8900A IC

2. PIC16C74 IC

Embedded Ethernet board enables microcontroller based projects to

communicate over 10baseT Ethernet.

Any controller that has two 8-bit bidirectional I/O ports can use this board.

IMPLEMENTATION OF BOARD

Collecting the components

of correct specification

Draw the circuitry on the PCB

using the automated board

design software

Place the IC, crystal and various

components in the PCB

Embed the program for interface

into the IC PIC16C74


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COLLECTION OF COMPONENTS

Quantity Part

1 Crystal CS8900A-CQ

1 Valor ST7011/ST7010T

2 24.9 Ohm

1 100 Ohm

2 680 Ohm resistor

1 4.7K Ohm

1 4.99K

1 68pf Cap

9 .1 mfd Cap

1 Link LED (Green)

1 LAN LED (Red)

1 20Mhz crystal

1 RJ45 Connector

1 Right angle header


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THE PIN DIAGRAM 0F IC CS8900A


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CONNECTIONS

16 pins of IC CS8900A is connected to the PIC16C74.

8 pin data bus

4 pin address bus

4 pin control pins

4 pins are connected with the RJ45 Connector to connect this IC with the

ether cable.

This board is supplied with a 5V power supply.

CRYSTAL CS8900A IC

It is the heart of our Embedded Ethernet board

Low cost ,Powerful Ethernet controller

It has the 4 K B integrated memory allowing it to receive and send the

packets asynchronous to microcontroller.

Crystal has an 8 Bit mode allowing it to interface to microcontroller.

There is no capacitor in the IC CS8900A.

Default setting of the CS8900A is I/O mode

Interrupts in 8 BIT mode are not supported. So we are using the polling

process for checking the interrupts.

POLLING OVER INTERRUPTS

Polling is the process of repeatedly asking the chip if any events has

occurred

CS8900A chip offers the choice of polling when notifying of events like

incoming packets


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Interrupts are another method like polling. Until now interrupt process is

used for checking the incoming events

Interrupts are a way of notifying the surrounding circuitry of an event when

occurs.

If interrupts are used, under heavy traffic, ISQ (interrupt service queue)

register will break. So interrupt line will stop going active.

If we use polling process this type, of registry breaking will not happen.

CS8900A CHECKING

To ensure that the CS8900A is connected & Packetpage pointer value is

0x3XXX

Test that the most significant byte is = 3:

1) Address = PacketPage Pointer = 0x000a

2) Enable AEN pin and IOR pin

3) ValueL = DataPin[8]

4) Disable AEN pin and IOR pin

5) Address = PacketPage Pointer + 1 = 0x000b

6) Enable AEN pin and IOR pin

7) ValueH = DataPin[8]

8) Disable AEN pin and IOR pin

9) Check ValueH[7 to 4] = 3, to indicate a good connection

8-BIT MODE

I/O mode is the default configuration and is enabling after reset.

To access the CS8900A in 8-bit mode, 8 I/O ports are used. Each I/O port

is 16 bits.

The following table gives a brief summary of each port:


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Offset Type Description

0x0000 Read/Write Receive/Transmit

Data0x0002 Read/Write Receive/Transmit

Data

0x0004 Write Transmit Command

0x0006 Write Transmit Length

0x0008 Read Interrupt Status

Queue

0x000a Read/Write PacketPage Pointer

0x000c Read/Write PacketPage Data

0x000e Read/Write PacketPage Data

INITIALISING THE CS8900A

Before any operation can be performed, the CS8900A must be configured

at power up or after a reset.

For each reset, the chip checks whether EEPROM is present or not

If the EEPROM is present, it can be used to initialize the CS8900A. Other

wise default configuration is loaded in the registers.

PIC16C74

PIC PERIPHERAL INTERFACE CONTROLLER

It is the backbone of the embedded Ethernet board.

It has the 40 pins.

Within the 40 pins, we need only 16 I/O pins.

3 pins for short of interfacing to the board.


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PORT A has 5 pin wide

The PIC drives the Embedded Ethernet board and implements some very

basic TCP/IP functionality.

The PIC doesn't really have the SRAM needed to fully implement even a

minimal TCP/IP stack but the application can be specialized to a particular

task (such as reading transducers).

Windows Sockets program is included that connects to the test circuit,

who is listening on UDP port 7 (echo). The echo service sends back any

data that it receives.

The programs are all setup to use IP address and Ethernet address (also

called an OUI- Organizationally Unique Identifier) of any address number

sequence. Since these are fictitious numbers, you may need to change

them.

For examples IP address 192.168.1.2 , Ethernet address-

00:00:00:12:34:56


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THE CIRCUIT DIAGRAM

PROGRAMMING THE IC

Program the microcontroller in the circuit through a parallel attachment to

pc.

Controller drives the embedded ether board and implements TCP/IP

functionality.

LOADING THE CODE


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Write the program in C language or any other.

Compile it using the compiler.

Using the simulators produce the error free program.

Using interfacing kit and driver transfer the program to the IC .

Run this program at command prompt.

This program will send five packets to the board, and the board will send

them back to the program for testing and then display it.

WORKING

Packet is a physical structure that is transmitted over the Ethernet LAN.

The packet includes the Preamble, Destination Address, Source Address,

Frame Type, Frame data, CRC.

Destination Source Frame

Preamble Address Address Type Frame data

C R C

8 octets 6 octets6

octets2 octets 64-1500 octets 4 octets

Frame - portion of the packet that contains data to be sent.

Preamble- contains alternate 1s & 0s for synchronization.

CRC- Cyclic Redundancy Check for error detection.

Internal registers of CS8900A are accessed by the Packetpageconfiguration.

The default configuration of the crystal is I/O mode.

To access the CS89000A in 8 bit mode 8 I/O ports are used. Each I/O port

is 16 bit


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PACKET TRANSMITTING

Writing the transmit command to the CMD port and the length to TX length

port, ST register is checked.

PIC16C74 sends the address enable (AEN) control signal to the CS8900A

for checking the transmitting memory for free space.

If space is available, CS8900A sends a write (WR) control signal to the

PIC IC.

Then PIC begin to writing the data in the order of a data at a time, to

Receive/Transmit data port 0

The data is transmitted to the transmitting memory through the 8BIT data

bus.

CS8900A sends the data to the Ethernet line to destination, at the traffic

free time.

PACKET RECEIVING

Polling process is used for checking the incoming signal.

This process is continuously going on until an event is occurred.

If the packet is available in the Ethernet, then the CS8900A gets in thepacket and store in the receiving memory.

CS8900A sends destination address of the packet to the PIC16C74

through the 4BIT address pin.

PIC16C74 compares the packet address with the already stored address

in the program.


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If the address is matched, then the PIC16C74 sends the read control

signal to the CS8900A.

CS8900A strips the preamble field in the Ethernet packet that is received.

Then the remaining of the packet is sent to PIC IC through the 8BIT data

bus.

This PIC16C74 picks up the data in that packet and then transmit in to the

host system.

UDP (echo or ack)

This is one of the TCP/IP functionality

This is for checking the remote host is alive or not.

For this, the system sends a signal to PIC IC

IC processes it & produces an echo signal, and spreads out in ether

If the remote host is alive, then it receives the signal, and sends back

acknowledgement to the transmitting end.

The transmitting end receives the signal and conforms that the remote

host is alive.

Similarly we can implement any basic TCP/IP functionality by

programming the IC.

APPLICATIONS

We can use this where the TCP/IP functionalities are required.

Embedded Ethernet boards can be mostly used in LAN technology.

They can be used for accessing remote appliances.

The data loss in this technology is very minimum.


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It is applied where the data security is required because the internal

registers are accessed by packet page configuration.

CONCLUSION

Ether technology has wide applications in the Local Area Network.

Ethernet board designed by embedded PIC IC makes handling the board very

easy. The program of the IC can be changed according to our requirements.

Since this board is used to determine whether a particular host is alive or not &

acknowledgements can be issued, this board on LAN enables fast signal transfer

between computers and we can perform many operations on remote appliances,

and thus making the communication reliable.

REFERENCES

INTERNETWORKING WITH TCP/IP VOLUME I

-DOUGLAS E.COMER CCNA STUDY GUIDE

-TODD LAMMLE

COMPUTER NETWORKS

-ANDREW S.TANENBAUM

www.embedded.com

www.embeddian.com

www.ethernet.com

www.esmertec.com
http://www.embedded.com/http://www.embeddian.com/http://www.ethernet.com/http://www.embeddian.com/http://www.ethernet.com/http://www.embedded.com/

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