giao tiep may tinh, Bài giảng RS232 - phần 2
1 Serial Communication EIA RS232, RS422 and RS485 Recommended Standard 232 The purpose of this course note is to attempt to describe the main elements in Serial Communication. This application note attempts to cover enough technical details of RS232, RS422 and RS485. EIA - Electroonic Industries Association Must be a Sender and Receiver A protocol is a set of rules which governs the transfer of data between computers. Protocols allow communication between computers and networks. Handshaking is used to establish which protocols to use. Handshaking controls the flow of data between computers Protocols will determine the speed of transmission, error checking method, size of bytes, and whether synchronous or asynchronous Examples of protocols are: RS-232, TCP/IP, Characteristics of Communication Systems 5 Basic Components Every communication system has 5 basic requirements •Data Source (where the data originates) •Transmitter (device used to transmit data) •Transmission Medium (cables or non cable) •Receiver (device used to receive data) •Destination (where the data will be placed) 5 Basic Components - simplex: One direction only Transmission Direction Half Duplex Transmission half duplex: Both directions but only one direction at a time Full Duplex Transmission full duplex: send and receive both directions at once RS232 Analog ADC Line coding Digital transmission Sampling Quantization Coding RZ, NRZ, AMI ASK, FSK, PSK Block diagram for digital transmission system Before any digital signal can be transmitted (via transmission medium or wireless) it must undergo line coding. What is line coding?? PCM 9 We are here Line Coding Pulse-code modulation (PCM) is a digital representation of an analog signal where the magnitude of the signal is sampled regularly at uniform intervals, then quantized to a series of symbols in a numeric (usually binary) code. Analog Data, Digital Signals PCM Procedures 10 September 2012 10 Pulse-amplitude modulation, acronym PAM, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. Sampled signal (discrete signal): discrete time, continuous values. Quantized signal: continuous time, discrete values Digital signal (sampled, quantized): discrete time, discrete values. Quantization is the procedure of constraining something from a relatively large or continuous set of values (such as the real numbers) to a relatively small discrete set (such as the integers). [...]... parity bit are considered for finding parity bit value Example for Even parity : 010 1 010 1 0, total 4 ones Example for Odd parity : 010 1 010 1 1, total 5 ones Even Parity Communication Concepts Any transmission May be: • Analog or Digital • Serial or Parallel Graham Betts Parallel Transmission Sender transmitted 1 0 0 1 1 0 0 1 All bits are sent simultaneously Receiver received -Each bit has it’s own piece... Serial Transmission Data is transmitted, on a single channel, one bit at a time one after another 1 0 0 1 1 0 0 1 Sender transmitted Receiver received Serial Transmission Shift Register Serial Transmission Synchronous Communication Clock Data 0 1 0 1 0 0 1 1 Asynchronous Communication 0 Start bit 1 0 1 0 0 0 1 1 1 Stop bit Serial Communication Name Sync Type /Async Duplex Max RS-232 async peer RS-422 async... including ground) (feet) full 2 11 5.2 30 2 (or 4 with HW handshake) half 10 10 000 4,000 1 (unidirectional only, additional pins for each bidirectional comm.) RS-485 async multi-point half 32 10 000 4,000 2 I2C sync multimaster half Limitation based on bus capacitance and bit rate 3400 10 00 625 master/slav half e Limitation based on bus capacitance and bit rate 16 Microwire sync 1- Wire async for every slave if slave count is more than one) . (usually binary) code. Analog Data, Digital Signals PCM Procedures 10 September 2 012 10 Pulse-amplitude modulation, acronym PAM, is a form of signal modulation. 1 Serial Communication EIA RS232, RS422 and RS485 Recommended Standard 232 The purpose of