techkriti lecture series communication by: ashutosh kumar
TRANSCRIPT
TECHKRITI LECTURE SERIES
CommunicationBY:
Ashutosh Kumar
COMMUNICATION
SCOPE OF COMMUNICATION
Telephones and Cell Phones
SCOPE OF COMMUNICATION
Internet
Wireless networks
SCOPE OF COMMUNICATION
SCOPE OF COMMUNICATION
Satellite Networks
ESSENTIALS OF COMMUNICATION
But this simple model requires many guarantees.
Sender Receiver
Communication Link
Data
GUARANTEES IN COMMUNICATIONS
The communication link exists. The communication link is sound. The sender and receiver are the correct
nodes. The sender is sending the correct data. The receiver is able to correctly interpret the
incoming data.
PROTOCOLS IN COMMUNICATION
The standard rules that defines the
parameters of communications and ensures these guarantees are called protocol.
ADVANTAGES OF PROTOCOLS
Standardized, so interoperability is ensured. Usually include error-detection and error-
correction mechanisms. Are available as implemented chips that can
be directly used.
TYPES OF PROTOCOLS
There are different ways of categorizing protocols
First Categorization :
Second Categorization :
Serial Mode Transfer
Parallel Mode Transfer
Synchronous Mode
Transfer
Asynchronous Mode Transfer
SERIAL AND PARALLEL MODE
SENDER
RECIEVER
SERIAL MODE
PARALLEL MODE
SERIAL VS PARALLEL MODE
Parameter
ReliabilitySpeedPowerCostComplexityRange
Serial Mode Parallel Mode
Reliable UnreliableSlow FastLow High
Low High High LowLong Short
Serialiser/Deserialiser
SYNCHRONOUS AND ASYNCHRONOUS MODE
Pertains to sender-receiver synchronization. Sender sends data at a certain speed. For
flexibility, protocols allow for multiple speeds.
NEED OF SYNCHRONIZATION
SENDER1
0
1
0
1
0
1T
RECEIVER
T/2
1 1
0 0
1 1
0 0
1 1
0 0
1 1
Suppose Sender sends data with a Time Period of T
What if Receiver doesn’t know the speed and assume it to be say T/2
The Data received will be
SYNCHRONOUS MODE Sender sends a clock signal along with data at
every rising / falling edge of the clock, the data value is read by the receiver.
SENDER
SENDER CLOCK
RECIEVER 0 1 0 1
0 1 0 1
ASYNCHRONOUS MODE
There is no clock signal. The receiver and the sender communicate at
a predetermined speed (bauds or bits per second).
Baud Rate : Baud Rate is a measurement of transmission speed in asynchronous communication.
The devices that allows communication must all agree on a single speed of information
'bits per second'.
SYNCHRONOUS VS ASYNCHRONOUS MODE
Parameter
ReliabilityCostComplexity
Synchronous Asynchronous
Reliable Error ProneExpensive InexpensiveComplicated Simple
TRANSMISSION MODES
SENDER RECIEVER
Simplex
Only one way transmission takes place
TRANSMISSION MODES
SENDER RECIEVER
Half-Duplex
Two way transmission takes place but only one end can communicate at a
time
TRANSMISSION MODES
SENDER RECIEVER
Full-Duplex
Two way transmission takes place and both end can communicate
simultaneously
WIRED
WIRELESS
SERIAL COMMUNICATION
POPULAR SERIAL COMMUNICATION STANDARDS
RS-232 (using UART) Serial peripheral interface (SPI) System management bus (SMBus) Serial ATA (SATA) UART: Universal asynchronous receiver/transmitter
ASYNCHRONOUS SERIAL COMMUNICATION TERMS
Start bit—indicates the beginning of the data word Stop bit—indicates the end of the data word Parity bit—added for error detection (optional) Data bits—the actual data to be transmitted Baud rate—the bit rate of the serial port Throughput—actual data transmitted per sec (total bits transmitted-overhead) Example: 115200 baud = 115200 bits/sec If using 8-bit data, 1 start, 1 stop, and no parity bits, the effective throughput is: 115200 * 8 / 10 = 92160 bits/sec
ASYNCHRONOUS SERIAL COMMUNICATION
Serial communication implies sending data bit by bit over a single wire
Asynchronous transmission is easy to implement but less efficient as it requires an extra 2-3 control bits for every 8 data bits.
This method is usually used for low volume transmission
CONNECTIONS
Device1 RX TX GND
TX Device2RXGND
ERROR DETECTION
•Parity bit is HIGH when number of 1’s in the Data is odd.
•Respectively, it is LOW when number of 1’s in the Data is even
CODING
Two simple commands : putchar(char); sends 8-bit characters through UART getchar(); receives 8-bit characters via UART
WHERE TO CODE
TRANSMITTER CODE
RECIEVER CODE
ANY QUESTIONS THIS FAR?
WHAT IS A X-BEE
XBee is the brand name from Digi International for a family of form factor
compatible radio modules.
HOW DOES THE XBEE WORK / HOW TO CONTROL IT?
Every XBee works as a wireless serial connection (or -network) and can be used like a normal COM port.
You can easily hook up the XBee to a laptop or an arduino and you can send and receive data over long range. In fact, the only thing you need to do is connect power and connect one wire to the XBee for data receive or data send (or two if you want both).
HOW TO CONFIGURE XBEE USING X-CTU?
XCTU is a small utility program written by Digi/Maxstream.
You can download this utility from the Digi website, www.Digi.com , under Supports/Drivers.
Download the latest drivers onto you PC.
HOW TO PROGRAM A XBEE
Connect the Xbee to the usb wireless module or the breakout board or Xbee Explorer.
Connect the board to the PC/laptop. Open X-CTU. And select PC Settings Tab from the Tabs
Menu on the top of the page.
QUERY
1. Select USB COMM. Port to the value of A-B Cable, display in the Device Manager setting.
2. Set the setting to the values of A-B Cable. 3. Click the Test/Query button 4. If the Com test / Query Modem dialogue appear with
an error message: Check if you have set the baud rate, flow control, data bits, parity and stops bits in the dialogue same as the Cable settings.
5. If everything goes well, you will see the dialogue displayed as in step 4 in the picture below. You should take note of the firmware version displayed in the dialogue. This is important for upgrading your firmware later. Then click OK.
Now, let's move on to do the configuration on the XBee.
1. Select the Modem Configuration Tab on the Main Tab Menu. 2. Click Read button, if this is your first time running the XCTU software, you will see the Question dialogue appear, and it asks if you want to update the configuration files, which is recommended. 3. If you click Yes button, You will see the Get new versions dialogue pop up
1. Then click the Web/file button. XCTU will start loading all the available firmware to your PC. 2. When XCTU is done with uploading, click the Done button. The Update Summary dialogue will pop up, displaying all the firmware for the XBee module. 3. Click OK.
Baud Rate
1. With the Modem Configuration Tab Menu still selected, 2. click the Read button again. You will see all the current settings show up in the display area. 3. Scroll down to find Serial Interfacing folder. 4. Change the baudrate to 57600 bit/s. (This is the prefered value we are using .You can use any value you like.) 5. Click the Write button, (the one next to Read button), to save the setting.
PAN ID
• To set the PAN ID or Personnal Area Network ID, which is the unique number to assign to XBee so XBee can talk to the right Xbee in the same Network Area.
• For example, if you are building a robot, and using only two XBees to communicate to each other, and you may want to avoid others that also using XBees for communication to be in the same Network Area.
• You can specify any number from 0000 to FFFF for your PANID. The factory PANID default value is 3332.
1. Still select the Modem Configuration Tab, 2. scroll up to the top of display area, 3. Click at the PAN ID to change the value. 4. Then click the Write button again to save the PAN ID setting to the XBee flash memory.
Ready to use
• Now, you are set, the XBee modem is ready to use.
• If you have another XBee, you can repeat the steps to configure the modem.
• You are now ready to move to the next step for upgrading the firmware.
• In case, you want to update your XBee firmware without using the XCTU utility program, you can use the Terminal program to do that as well.
SPI – SERIAL PERIPHERAL INTERFACE
SPI
Serial ?? Because it works on serial mode of transfer.
It is also synchronous and full duplex. Peripheral Interface. Because it has the capability of communicate
with many nodes. How?? Let us see.
SPI
In SPI, the sender and receiver follows a master-slave relationship.
There may be multiple nodes in the network. One node is master, the rest are slaves. The communication is always initiated by the
master. The slaves can communicate only with the
master. How do master selects the slave??
SPI SCHEMATICS: SINGLE SLAVE
SPI PINS
CLK is generated by Master and is used as the mode is synchronous.
MOSI is Master Out Slave In: Data sent by Master to Slave.
MISO is Master In Slave Out: Data sent by Slave to Master.
SSSS is slave select: Slave communicates with Master only if this pin’s value is set as LOW.
SPI SCHEMATICS: SINGLE SLAVE
Note one thing, if you use a single slave, you could save yourself a pin by hooking up the SS pin on the slave to GND and the SS on the master to VCC.
SPI SCHEMATICS: MULTIPLE SLAVES
DATA TRANSFER IN SPI
M0
M1
M2
M3
M4
M5
M6
M7
S0
S1
S2
S3
S4
S5
S6
S7
MASTER SLAVE
MOSI MISO
DATA TRANSFER IN SPI
M1
M2
M3
M4
M5
M6
M7
S0
S1
S2
S3
S4
S5
S6
S7
M0
MASTER SLAVE
MOSI MISO
DATA TRANSFER IN SPI
M2
M3
M4
M5
M6
M7
S0
S1
S2
S3
S4
S5
S6
S7
M0
M1
MASTER SLAVE
MOSI MISO
DATA TRANSFER IN SPI
S0
S1
S2
S3
S4
S5
S6
S7
M0
M1
M2
M3
M4
M5
M6
M7
MASTER SLAVE
MOSI MISO
SPI IN ATMEGA 8
SPI CODING
SIMPLE SPI CODE
char data = SPITransmit(‘a’);
In case of master, the data is written on the register and send to the slave.
In case of slave the data is written on the register and it waits for the master to transmit the data, when it also transmits its own data.
MASTER CODE
DDRB = 0b10110000; // configure SPI Master Pins
ISR(INT0_vect){ // External Interrupt 0
data = SPITransmit(0x01); // when switch is pushed
// send data}
SLAVE CODE
DDRB = 0b10000000; // configure SPI Slave Pins
ISR(SPI_STC_vect){ // SPI Transceiver Interrupt data = SPDR ; // read the data if(data == 0x01){ PORTA = ~PORTA; // if data is correct toggle
Led }}
ANY QUESTIONS LEFT?
