tailieunhanh - DATA TRANSMISSION

Introduction Data into a computer (via a keyboard) is encoded by the electronics within the keyboard into an equivalent binary-coded pattern using standard coding schemes: Two most common schemes: EBCDIC (Extended Binary Coded Decimal Interchange Code): 8-bit code ASCII ((American Standards Committee for Information Interchange): 7-bit code | DATA TRANSMISSION Introduction Data into a computer (via a keyboard) is encoded by the electronics within the keyboard into an equivalent binary-coded pattern using standard coding schemes: Two most common schemes: EBCDIC (Extended Binary Coded Decimal Interchange Code): 8-bit code ASCII ((American Standards Committee for Information Interchange): 7-bit code Bit Transmission Parallel mode: uses several wires, each wire sending one bit at the same time as the others. Serial mode: sends bit by bit over a single line Serial mode is slower than parallel, but can be used over longer distances because the bits stay in the order they were sent, while bits sent in parallel mode tend to spread out over long distances. Parallel Transmission Serial Transmission Communication Modes Simplex: Used when data is to be transmitted in one direction only Half-Duplex: Used when the two interconnected devices wish to exchange information alternately (only one device can transmit at a time) | DATA TRANSMISSION Introduction Data into a computer (via a keyboard) is encoded by the electronics within the keyboard into an equivalent binary-coded pattern using standard coding schemes: Two most common schemes: EBCDIC (Extended Binary Coded Decimal Interchange Code): 8-bit code ASCII ((American Standards Committee for Information Interchange): 7-bit code Bit Transmission Parallel mode: uses several wires, each wire sending one bit at the same time as the others. Serial mode: sends bit by bit over a single line Serial mode is slower than parallel, but can be used over longer distances because the bits stay in the order they were sent, while bits sent in parallel mode tend to spread out over long distances. Parallel Transmission Serial Transmission Communication Modes Simplex: Used when data is to be transmitted in one direction only Half-Duplex: Used when the two interconnected devices wish to exchange information alternately (only one device can transmit at a time) Full-Duplex: Used when data is to be exchanged between the two connected devices in both directions simultaneously Transmission Modes For the receiver to decode and interpret bit pattern correctly, it must be able to determine The start of each bit cell period bit / clock synchronization The start and end of each elements (character / byte) character / byte synchronization The start and end of each complete message block frame synchronization Transmission Modes Asynchronous transmission: Transmitter and receiver clocks are independent Synchronous transmission: Transmitter and receiver clocks are synchronized Asynchronous Transmission Asynchronous Transmission In a steady stream, interval between characters is uniform (length of stop element) In idle state, receiver looks for transition 1 to 0 Then samples next seven intervals (char length) Then looks for next 1 to 0 for next char Simple Cheap Overhead of 2 or 3 bits per char (~20%) Good for data with large gaps .