The data transfer speed in RS-422 depends on the distance and can vary from 10 kbps (1200 meters) to 10 Mbps (10 meters). In the RS-422 network, there can only be one transmitting device and up to 10 receiving devices. The RS422 is similar to RS232 which allows to simultaneously send and receive messages on separate lines but uses a differential signal for this. Handshaking allows the transmitter and receiver device to agree before the communication is going to start.Refer from In this case, character ‘C’ is missed by the receiver. Buffer is a temporary storage location which allows the transmitter and receiver to store the data until the information is processed by each other at different speeds.Īs shown in above figure, If the transmitter sends data at a higher speed, the receiver may fail to receive. To send and receive the information without loss of data, it is necessary to maintain robust communication between the transmitter and receiver. Also, DTR and DSR are also connected in cross mode. To use the handshaking technique, RTS and CTS are cross-coupled. Other pins, RTS, CTS, DSR, and DTR are connected in loopback fashion. When no handshaking is performed, only the TxD (Transmitter) and RxD are cross-coupled. The connectors DB9 and Db25 are used for handshaking purpose. The messaging between transmitter & receiver can be done by handshaking. Handshaking is the process which is used to transfer the signal from DTE to DCE to make the connection before the actual transfer of data. The data format is initiated with a start bit followed by 7-bit binary data, parity bit and stop bit which are sent one after another. Here, no clock is required for synchronizing the transmitter and receiver. As RS-232 is a point-to-point asynchronous communication protocol, it sends data in a single direction. The working of RS-232 can be understood by the protocol format.
In null modem cable, the TX (Transmitter) pin of the male connector is linked up with the RX (Receiver) pin of the female and the RX pin of the male is connected to TX pin of the female. To make serial communication possible between DTE and DCE, two types of RS232 cables exist. It comes in DB9 connector which has 9 pinouts such as TxD, RxD, RTS, CTS, DTR, DSR, DCD, GND. The logical "0" (SPACE) corresponds to a voltage in the range from +3 to +15 V. The logical "1" (MARK) corresponds to a voltage in the range from -3 to -15 V. Information on the RS-232 interface is transmitted digitally by logical 0 and 1. The RS232 is point-to-point topology with maximum one device connected and covers distance up to 15 meters at 9600 bps. The RS232 comes in male and female connectors. The RS232 (Recommended Standard 232) is very common protocol used to connect different peripherals such as Monitors, CNCs etc. The well-known examples are RS-232, RS-422 and RS-485. On the receiver side, the receiver extracts the data using its own clock and convert the serial data back to the parallel form after stripping off the start, stop, and parity bits. Also it adds the start, stop and parity check bits. On the transmitter side, there is a shifting of parallel data onto the serial line using its own clock. In asynchronous Serial Interface the absence of external Clock Source makes it rely on several parameters such as Data Flow Control, Error Control, Baud Rate Control, Transmission Control and Reception Control. The Asynchronous Serial Interfaces can be seen in mostly in long distance applications and are a perfect fit for the stable communication.
In asynchronous Serial Interface, the external clock signal is absent. I2C supports transfer speed of around 100kHz (original standard, or 400kHz using the most recent standard). A bus is considered idle if both SDA and SCL lines are high after a STOP condition. Data transfer may be initiated only when the bus is idle. The I2C interface consists of a Serial Clock Line(SCL) and Serial Data Address(SDA). Each device on the I2C bus has a specific device address to differentiate between other devices that are on the same I2C bus. The data transmission always initiated by the master. It is half duplex, synchronous serial communication protocol. I2C is a serial 2 wire bus designed to communicate between the IC’s using a minimum number of pins. I2C interface is a simple bidirectional interface which uses a single data line to transmit and receive the data. When the master generates the clock and selects a slave the data can be transferred either in one or in both the direction simultaneously. Communication in SPI is done by a master and slave relationship, in which master initiates data frame.
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