Communication can be classified two types based on the clock..
1) Synchronous, 2) Asynchronous
1) Synchronous Communication:
=> uses a physical clock
=> Receiving and transmitting of data in synchronization with physical clock pulses..
=> Physical Clock decides the speed of the communication [Master produces a clock]..
=> Eg. I2C, SPI
A) I2C:
=> 2 line Communication [named SDA and SCL]
=> Half Duplex Communication because only one line for data [At a time only one can communicate For example Master is sending some data slave should not
interfere, After completion of sending slave has to respond]
=> Speed of the I2C i) Standard Mode [100kbits/sec], ii) Fast Mode [400kbits/sec], iii) Fast-Mode Plus [1Mbit/sec]
B) SPI:
=> Requires 4 lines.. [MOSI, MISO, CLK, CS]
=> Full Duplex [Separate Line for sending and Separate line for receiving]
=> Speed upto 40Mbps.. [More faster than I2C due to full duplex]
2) Asynchronous Communication:
=> Receiving & Transmitting of data takes place in accordance with the a virtual clock called baud rate [bits/sec].. Baud Rate is nothing but communication speed.
=> Baud Rate has to be fixed on both side of the system to be communicated with the same value.
=> Lower the Baud Rate then the distance can be larger..
=> Eg: RS-232, RS-485.
A) RS-232:
=> Differential Voltage Communication.
=> Full Duplex Communication.
=> It uses three wires namely TXD, RXD, COM.
=> Being a voltage communication limited to short distance only. [A maximum of 5 feet]
=> Being a voltage signal it is very much prone to noise like EMI, ESD.
=> Can be used with HandShaking mode [Optional]
B) RS-485:
=> Differential ended current communication.
=> Half Duplex & it requires only two wires namely DATA+, DATA- (or) A,B.
=> Being current communication can be used for longer distance 1.5km.
=> Being current communication very much immune to noise like ESD, EMI.
=> Being differential ended and twisted pair we have very high CMRR.
=> Baud rate is limited to 9600bps up to 1.2 km or 19200 baud rate with limited distance.