What is CAD Communication?

Need For Communication:

In complex embedded systems, multiple electronic systems are used for establishing the application. In this case, there is a need for the exchange of information between these electronic systems.

Types of communication:

1) Parallel Communication:

• Data is transmitted simultaneously on a separate wire.
• The space needed is higher, So the cost of implementation is high.
• Faster speed of communication.
• Requires complex wiring circuitry.
• Does not require synchronization between Sender and Receiver.

Example: PCI, ATA, Etc

 

2) Serial Communication - Information is transmitted as a series of bit streams one at a time.

1) Based on the number of paths/Wire, serial communication is classified as

• Half Duplex
• A single wire is used for transmission and reception of messages.
• Communication direction will be one at a time.

Full Duplex

• Dedicated wire/path for transmission and reception of data.
• Simultaneous data transfer for Transmission and Reception of data

Based on the type of synchronization

• Synchronous serial Communication:
• Dedicated wire for Data transmission and Clock Signal
• Follows master and slave-based communication
• Master – Generates clock irrespective of the direction of communication
• Slave – Follows the master clock to perform read/write operations on a data bus
• Examples of Synchronous Communication: SPI, I2C, USART, RS232, Etc 

Disadvantages of Synchronous serial communication:

• Clock from Master – High-frequency signal which might cause data interference and corruption.
• External noise due to EMC of the board might affect the clock characteristics, which could result in the wrong decoding of data.
• The transmitter and receiver should operate in same clock frequency.

Asynchronous Serial Communication:

• Sender and receiver have their own internal clocks thus do not need an external common clock pulse.
• Slower data transfer rate compared to synchronous communication
• Example : UART, CAN, LIN , Etc.
• Parameters of Asynchronous Communication:
• Baud rate – Number of data bits transmitted to receiver in 1 second, unit: Bits per Second(BPS)
• (Rule of Thumb: Transmitter and Receiver should have same Baud rate for proper communication
• Bit Duration: The time for which transmitter precisely maintains for every bit on a data bus or the time for the receiver to decode each bit on the data bus
• Bit Duration = 1/ Baud rate
• Idle State – Default state in absence of communication
• Number of Start and Stop bits: (Self Synchronization of TX and RX)
• For a proper communication synchronization is required, as sender and receiver run at different clock rate.
• So Start Bit and Stop bits are used for exact synchronization.
• This makes it slower as compared to that in synchronous transmission, but it is cheaper.

Example:

Simple Asynchronous communication :

• The baud rate for communication: is 9600bps
• Data to transmit: “1011 0111”

Working:

• When the Data in the BUS changes from continuous logic to Low(Start Bit), The internal timer of the sender and receiver starts and gets ready for communication.
• After data bits, when the bus level changes from logic low to high (Stop bits) to indicate the end of the communication.

The disadvantage of Asynchronous Serial Communication

• Start and Stop Bit Over heading.
• Noise in the signal may lead to False recognition of Start and Stop bits.
• Response time cannot be predicted.
• The handling of errors is more intricate.
• Applications are comparatively hard to design for such transmissions.