MIKROPROCESORY PRO VÝKONOVÉ SYSTÉMY. Serial Data Transmission (Stručný přehled) České vysoké učení technické Fakulta elektrotechnická

Transcription

1 MIKROPROCESORY PRO VÝKONOVÉ SYSTÉMY Serial Data Transmission (Stručný přehled) České vysoké učení technické Fakulta elektrotechnická Ver.1.10 J. Zděnek, 2017

2 Serial data transfer - principle Serial data transfer means transmission of one bite in particular time. Clock signal have to be synchronized between Transmitter and Receiver. Advantages of serial data transfer: Lower number of wires required. Immunity against EMI. Disadvantages of serial data transfer : Slower that parallel data transfer. Advantages of parallel data transfer : Faster than serial data transfer. Disadvantages of parallel data transfer : Greater number of wires required for data. EMI vulnerability on longer distances. A1B14MIS Mikroprocesory pro výkonové systémy 12 2

3 Serial data transfer - principle A1B14MIS Mikroprocesory pro výkonové systémy 12 3

4 Serial data transfer - principle Device 1 Device 2 Serialization Data line Paralelization A1B14MIS Mikroprocesory pro výkonové systémy 12 4

5 Serial data transfer - synchronization Various types of serial data transfer methods. There have to be clock signal between transmitter and reciever. Basic principles of serial data transfer: Asynchronous, synchronization of the transfer by Start bitu. Synchronnous, separate line for Clock signal. Synchronous, clock signal mixed with data clock signal is derived from data signal (from signal edges). A1B14MIS Mikroprocesory pro výkonové systémy 12 5

6 Serial data transfer - asynchronous Start bit Asynchronous data A1B14MIS Mikroprocesory pro výkonové systémy 12 6

7 Serial data transfer - synchronous Synchronous, separated Clk A1B14MIS Mikroprocesory pro výkonové systémy 12 7

8 Sériový přenos synchronní (hodiny v datech) Data coding have to have enough edges to code Clk Synchronous, mixed Clk A1B14MIS Mikroprocesory pro výkonové systémy 12 8

9 Serial data transfer speed Transmission speed is important for serial data transfer. Speed is derived from bit period T - time, to transmit 1 bit information. Transmission speed v is calculated in (bps bits per second) Baud [Bd] where bps = Bd * počet přenesených bitů za vteřinu A1B14MIS Mikroprocesory pro výkonové systémy 12 9

10 Serial data transfer speed Serial data T = bit period Speed v= 1/T [bps] Bits per second A1B14MIS Mikroprocesory pro výkonové systémy 12 10

11 Bit coding - NRZ A serially transmitted bit can be coded in a different way. Different coding has different immunity to interference, different sync properties (number of edges in the signal) and different complexity of implementation on both the transmiting and the receiving side. NRZ (Non Return to Zero) bit encoding It is level coding (1 = higher level, 0 = lower level) When transmitting bits of the same level, there are no edges in the signal and synchronization on the receiving side (with a larger number of the same bits) is difficult. NRZ encoding is used, for example, in a UART transmitter (see below), where each character (i.e., a short set of bits) is synchronized again with the so-called "Start bit". A1B14MIS Mikroprocesory pro výkonové systémy 12 11

12 Bit coding - NRZ A1B14MIS Mikroprocesory pro výkonové systémy 12 12

13 Bit coding - NRZI NRZI (Non Return to Zero Inverted) encodes bit level 1 edge and bit level 0 with no line state change (see next slide). This bit encoding method reduces the bandwidth transmission bandwidth requirement (compared to NRZ), but there are no edges in the signal when transmitting a sequence of zero (receiver synchronization problem). Bit stuffing / destufing is the method where the value is inverse (e.g., after 5 nulls) and at the receiver is the inverse value again taken away. This method guarantees a sufficient number of edges to synchronize the receiver even with a long sequence of transmitted data of the same level.. A1B14MIS Mikroprocesory pro výkonové systémy 12 13

14 Bit coding - NRZI A1B14MIS Mikroprocesory pro výkonové systémy 12 14

15 Bit coding Manchester Phase coding (Manchester) immune against interferrence. Rising edge is coding 1, falling edge 0. This coding produces enough edges to code clock signal. Phase coding (Manchester) has disadvantage in required higher bandwidth than NRZ. A1B14MIS Mikroprocesory pro výkonové systémy 12 15

16 Bit coding Manchester A1B14MIS Mikroprocesory pro výkonové systémy 12 16

17 Bit coding MLT3 MLT3 three level NRZI coding. Value 1 is coded as closest edge, value 0 is coded as reamining level. Used for 100Mbps Ethernet Disadvantage is more complex HW part of transmitter and reciever. A1B14MIS Mikroprocesory pro výkonové systémy 12 17

18 Bit coding MLT3 A1B14MIS Mikroprocesory pro výkonové systémy 12 18

19 Bit coding MLT3 A1B14MIS Mikroprocesory pro výkonové systémy 12 19

20 Connection topologies Point-to-Point Point to Point connection of two devices. Half Duplex only one wire for data. One device can receive and second transmit in particular time Full-Duplex separated lines for transmitting and receiving data. A1B14MIS Mikroprocesory pro výkonové systémy 12 20

21 Connection topologies Point-to-Point Half-Duplex Full-Duplex A1B14MIS Mikroprocesory pro výkonové systémy 12 21

22 Connection topologies Bus Common Bus (Bus) several devices connected to one bus. Half-Duplex only one device can transmit and others have to recive. Time sharing of bus necessary (Half-Duplex). (Bus Access) can be controlled in several ways (Master-Slave, Multi-Master). A1B14MIS Mikroprocesory pro výkonové systémy 12 22

23 Connection topologies Bus Vždy Half-Duplex..... A1B14MIS Mikroprocesory pro výkonové systémy 12 23

24 Connection topologies Star Star more devices connected to Hub or Router or Switch Hub transmits data to connected devices Connection to Hub is both Half-Duplex and Full-Duplex. Star topology uses USB or Ethernet. Star connection can be done by optical fibres. A1B14MIS Mikroprocesory pro výkonové systémy 12 24

25 Connection topologies Star Full Duplex or (Half Duplex) Hub (Router, Switch) A1B14MIS Mikroprocesory pro výkonové systémy 12 25

26 Connection topologies Loop Loop (Kruh) otuput of one device is connected to input of next device. Each device should have own receiver and own transmitter. Each device can subtract data from transmitted signal or pass them or add own data. Loop topology is used by EtherCat. A1B14MIS Mikroprocesory pro výkonové systémy 12 26

27 Connection topologies Loop A1B14MIS Mikroprocesory pro výkonové systémy 12 27

28 Common bus access Master-Slave Common Bus (Bus) - This connection method can only be used in Half- Duplex mode, when one of the devices is transmitting others can only receive. Master-Slave delegates Bus Time Sharing on Master devices. The master controls access to the bus, inviting a Slave device to transmit or transmit itself. The advantage of this organization is the good use of bus throughput (with the correct schedule of Masters). The disadvantage is the possibility of a malfunction of the master device, then no one organizes bus access and the whole system pauses. Adding of so called Weak-Master device, where this block monitors bus traffic, and when bus stops (for Master malfunction), it takes bus control (typically with limited functions). A1B14MIS Mikroprocesory pro výkonové systémy 12 28

29 Common bus access Master-Slave Master - Slave..... Master Slave 1 Slave n Weak Master A1B14MIS Mikroprocesory pro výkonové systémy 12 29

30 Common bus access Multi Master Common Bus (Bus) Half Duplex communication. Bus Access type Multi-Master takes all devices connected to bus as equal. CSMA/CD (Carrier Sense Multi Access/Collision Detection) all devices monitor bus communication, when there is no traffic they start to transmit. In case of collision all transmitting devices stops transmitting and generate random timeout. Used in CAN A1B14MIS Mikroprocesory pro výkonové systémy 12 30

31 Common bus access Multi Master Multi Master (CSMA/CD, CSMA/CR)..... Master 1 Master 2 Master n A1B14MIS Mikroprocesory pro výkonové systémy 12 31

32 Communication protocols The protocols (data formats) used for serial communication are very numerous. The individual protocols differ: Transfer rate. Structure of the transmitted data unit (Frame). Possible maximum distance between communicating devices. The way of encoding bits. Bus access method (if used by the bus). Type of transmission medium (wire, optical fiber). Resistance to interference (transmission errors). Other parameters. A1B14MIS Mikroprocesory pro výkonové systémy 12 32

33 UART Universal Asynchronous Receiver Transmitter UART (Universal Asynchronous Receiver Transmitter) - is present in almost every microcontroller that transmits and receives short data messages (typically 8 bits). These messages are called "Characters". Each character is given by Start Bit (0) and ends with a Stop Bit (1). The character may be supplemented by a parity bit sometimes with another bit distinguishing the meaning of the character (data, address). After sending a character, you can send another character or leave the line iddle. Each character is therefore synchronized to the receiving side by the Start bit. This type of transfer is called asynchronous. Between the communicating units, the baud rate is agreed by the programmer. UART uses bit encoding of the NRZ type. UART has a separate transmitter and receiver. No protocol for longer data is defined, user has to define itself. A1B14MIS Mikroprocesory pro výkonové systémy 12 33

34 UART Universal Asynchronous Receiver Transmitter UART works with voltage levels (0-5V or 0-3,3V) that are not suitable for long distance transmission. Therefore, level converters (Transmitter / Receiver) are used : RS232 - ground voltage. Transmission speed up to 250kbps, cable tens of meters for lower transmission speeds. RS422 - differential (twisted pair with termination impedances for transmission). The drive is not disconnectable (only Full-Duplex). Transmission speed up to 100Mbps, twisted impedance-terminated double-link, hundreds of meters high. RS485 - differential (twisted pair with terminating impedances for transmission). The driver is disconnectable and a common bus (Half- Duplex) can be organized. Transmission speed up to 100Mbps, twisted impedance-terminated double-link, hundreds of meters high. Current loop 4 / 20mA (ie 0/1) - very resistant to interference. Transmission rate up to 20kbps, cable hundred meters. A1B14MIS Mikroprocesory pro výkonové systémy 12 34

35 UART + RS232 A1B14MIS Mikroprocesory pro výkonové systémy 12 35

36 RS422 Differential driver (Twisted Pair) Full - Duplex A1B14MIS Mikroprocesory pro výkonové systémy 12 36

37 RS485 Switchable driver Master Slave Bus (Twisted Pair) Half - Duplex A1B14MIS Mikroprocesory pro výkonové systémy 12 37

38 SPI Serial Peripheral Interface SPI (Serial Peripheral Interface) - synchronous serial transmission with separate clocks. Master-Slave method. Master sends clocks and data, Slave is transmitting his data at the same time. The master activates Slave by setting the SS (Chip Select) signal. Full-Duplex transmission. Designed for short-distance communication (within a PCB). Transmission speed is high (max. 50Mbps). Transmission takes place by exchanging data between the shift registers in Master and Slave. Data can be 8 bits wide, some microcontrollers allow even greater data width (programmable). A1B14MIS Mikroprocesory pro výkonové systémy 12 38

39 SPI Serial to Peripheral Interface A1B14MIS Mikroprocesory pro výkonové systémy 12 39

40 SPI Serial to Peripheral Interface A1B14MIS Mikroprocesory pro výkonové systémy 12 40

41 SPI Serial to Peripheral Interface A1B14MIS Mikroprocesory pro výkonové systémy 12 41

42 I2C Inter Integrated Circuits Bus I2C - the bus is intended primarily for initial programming of integrated programmable circuits within one PCB (consumer electronics equipment, industrial equipments,...) I2C is a Master-Slave two-wire synchronous bus with the option of assigning additional master devices and passing bus control. Active Master sends clock (SCL) and data sends active device (master or slave) to SDA. Bus collectors are Open Collector type with Vcc (Pull-up Resistors) resistors. The master uses a 7-byte address. 6 addresses are reserved, so 112 devices can be addressed. The I2C bus is relatively slow: Transmission rates are 100kbps or 400kbps. Later in the standard added HS (High Speed) speed of 1.7Mbps. However, this speed requires active (half) Pull-up elements. A1B14MIS Mikroprocesory pro výkonové systémy 12 42

43 I2C Inter Integrated Circuits Bus Master-Slave Open Collector Bus Microcontroller A1B14MIS Mikroprocesory pro výkonové systémy 12 43

44 I2C Communication Protocol A1B14MIS Mikroprocesory pro výkonové systémy 12 44

45 MIKROPROCESORY PRO VÝKONOVÉ SYSTÉMY Sériový přenos informace (Stručný přehled) Konec České vysoké učení technické Fakulta elektrotechnická