Signals - Sensors 3 Lecture Notes PDF

Signals – sensors 3. Dr. Gyányi Sándor  Overview of digital interfaces ▪ The handling of binary values needs multiple bits to be written or read simultaneously. ▪ Multiple bits mean multiple pins and wires. ▪ These wires form „bus”. ▪ A processing unit can communicate with other units...

Signals – sensors 3. Dr. Gyányi Sándor  Overview of digital interfaces ▪ The handling of binary values needs multiple bits to be written or read simultaneously. ▪ Multiple bits mean multiple pins and wires. ▪ These wires form „bus”. ▪ A processing unit can communicate with other units on this bus. ▪ A bus can be serial or parallel. Signals - Sensors  Transmission techniques Two methods: ▪ Baseband: converting data bits into electrical or optical pulses, without modulation. ▪ Broadband: modulating the carrier signal’s frequency, amplitude or phase depending on the data bits. Signals - Sensors 3  Baseband ▪ Two main techniques: ▪ Return-to-Zero (RZ): signal’s amplitude always returns to zero state within the symbol period. ▪ Non-Return-to-Zero (NRZ): signal’s amplitude does not return to zero state within the symbol period. ▪ Assign physical states to transmitting logical states (for example, 5V represents logical „1” value). ▪ The other logical state represented by 0v (unipolar coding) or negative value (bipolar coding). ▪ Problem: syncing the bitrate clock of the source and destination. Signals - Sensors 4  Unipolar RZ coding ▪ Bit „1” state represented by „+A” physical state (in the picture +1V). ▪ Bit „0” state represented by 0V. ▪ In the middle of symbol period the physical state always returns to 0V. ▪ Problem: data containing all „0” bits cause permanent 0V physical state. Impossible to synchronize the clock. Signals - Sensors 5  Polar RZ coding ▪ Bit „1” state represented by „+A” physical condition (in the picture +1V). ▪ Bit „0” state represented by „-A” physical condition (in the picture - 1V). ▪ In the middle of symbol period the physical state always return to 0V. ▪ Advantage: the line’s condition changes in every bits. Synchronization is relatively easy. Signals - Sensors 6  Unipolar NRZ coding ▪ Bit „1” state represented by „+A” physical state (in the picture +1V). ▪ Bit „0” state represented by 0V. ▪ Problem: no physical condition change in case payload data contains „1” or „0” bits only. Signals - Sensors 7  Polar NRZ coding ▪ Bit „1” state represented by „+A” physical condition (in the picture +1V). ▪ Bit „0” state represented by „-A” physical condition (in the picture -1V). ▪ Problems are the same as unipolar NRZ coding. Signals - Sensors 8  Alternate Mark Inversion (AMI) coding ▪ Bit „1” state represented by „+A” and „-A” physical condition (in the picture +1V and -1V). ▪ Bit „0” state represented by 0V. ▪ Polarity inverting in two consecutive „1” bits. ▪ Problem: synchronization impossible in case of data streams containing „0” bits only. Signals - Sensors 9  Manchester coding ▪ Bipolar coding (in the picture +1V and -1V). ▪ „0” bits represented by a falling edge in the middle of symbol period. ▪ „1” bits represented by rising edge in the middle of symbol period. ▪ Every bit state has falling or rising edge, provide easily synchronization. ▪ Average value of the line would be 0V. Signals - Sensors 10  Differential Manchester coding ▪ Difference to Manchester coding: in case of „0” bits, the direction of the edge in the middle of symbol period does not change. ▪ In case of „1” bit, the direction of edge inverting (if the previous edge was falling, the actual direction would be rising). Signals - Sensors 11  Parallel bus ▪ More than 1 bit can be transferred simultaneously. It needs as many wires as bits (for example 8 wires for 1 byte), plus synchronizing line. ▪ Transfer speed is significantly higher than in serial bus, but needs more wires and has limited length. ▪ Typical usage: communication between memory chips and microprocessors (DDR4 SO-DIMM memory modules have 256 pins). Signals - Sensors  Serial bus ▪ Data bits will be transferred from source to destination sequentially, in one wire. ▪ Separating these bits or higher layer communication units (bytes, words, frames) can be difficult. ▪ Asynchronous bus: data line itself contains information for detecting and separating data bits. For example: UART (RS232C interface), USB, 1Wire. ▪ Synchronous bus: it using a separated synchronizing line (clock). For example: SPI, or I2C interfaces. Signals - Sensors  Shift register in serial communication ▪ A digital shift register is a sequential logic circuit that is used to store and shift data. ▪ It consists of flip-flops connected in series, where each flip-flop stores a single bit of data. ▪ The main function of a shift register is to move data (bits) from one flip-flop to the next with each clock pulse. ▪ There are different types of shift registers: ▪ Serial in – serial out. ▪ Parallel in/out – serial in/out (different combinations are used in different applications). Signals - Sensors Shift register with parallel input Signals - Sensors  SPI (Serial Peripheral Interface) ▪ Full-duplex synchronous serial communication. ▪ Designed by Motorola. ▪ Relatively high data speed, short distance. ▪ Master-slave communication model, master generates communication clock (up to 50Mbit/s). ▪ Four-wire interface. ▪ MOSI: Master Output, Slave Input (SDO). ▪ MISO: Master Input, Slave Output (SDI). ▪ SCLK: Serial Clock (output from master). ▪ SS: Slave Select (for multi-slave configuration). Signals - Sensors  SPI interface model ▪ SPI interface contains two shift registers. ▪ Both master and slave send and receive data at the same time. MISO SHIFT SHIFT register register MOSI Clock SCLK generator SS Signals - Sensors  Slave Select ▪ Master enables communication with slave by Slave Select signal. ▪ If a slave device is inactive (Slave Select is high), its output (MISO) will go to high impedance state. ▪ Multiple slave devices can connect to master, but only one device can be in active state. ▪ Master selects the active slave by providing active state on the corresponding Slave Select pin. ▪ Always the master provides the serial clock. In dsPIC this means, user program must write data to SPI output register. Signals - Sensors  Multi slave configuration MOSI SCLK MISO SLAVE1 ▪ Master starts data transfer by providing SS1 MASTER active level on the corresponding slave SS2 select. SS3 ▪ Master provides serial clock and sends data to selected slave. SLAVE2 ▪ Every clock cycle a bit sending and receiving occurs in the same time. SLAVE3 Signals - Sensors Communication Signals - Sensors  I2C (Inter-Integrated Circuit) ▪ Developed by Philips, synchronous serial, half-duplex, multi-master, multi-slave protocol. ▪ Uses 2 bidirectional lines: SDA (Serial Data Line) and SCL (Serial Clock Line). ▪ Instead of independent slave select signals, device addresses are used to communicate with multiple devices. ▪ Advantages: Fewer wires, supports multiple devices in the same bus. ▪ Disadvantages: Slower than SPI. 100kbit/s, 400kbit/s were originally the standards, but faster speeds (up to 5Mbit/s) are available. ▪ More complex due to addressing and half-duplex communication. Signals - Sensors  I2C (Inter-Integrated Circuit) design ▪ All devices on the bus have a 7 bit address (10 bit addresses also available). ▪ Multiple master devices can control the bus. ▪ All target (slave) nodes are listening to the communication, but the device with the target address must be responding. ▪ There are 4 different modes: ▪ Master transmit: Controller node is sending data to a target (slave). ▪ Master receive: Controller node is receiving data from a target. ▪ Slave transmit: Target node is sending data to the controller (master). ▪ Slave receive: Target node is receiving data from the controller. Signals - Sensors  I2C (Inter-Integrated Circuit) signals ▪ Different signal levels assigned to „1” and „0” bits. ▪ When the bus is inactive, both SDA and SCL lines are in HIGH state. ▪ SDA must be examined after the SCL rise to HIGH state. ▪ There are two special signals: ▪ START condition: SDA is pulling LOW while SCL remains in the HIGH state. ▪ STOP condition: SDA is pulling HIGH while SCL remains in the HIGH state. ▪ After the START condition, data can be transferring from the master to the slave devices. ▪ First data byte contains the slave device address and a R/W bit. Signals - Sensors  I2C (Inter-Integrated Circuit) communication ▪ Master send the START condition, the address and the R/W bits. ▪ When master writes to the slave, the slave must generate an ACK or NAK bit after the received byte. Master must provide an extra clock for this bit. ▪ When master reads from the slave, the master must generate an ACK or NAK bit after the received byte. ▪ Master can generate a START condition during the data transmission. This called REPEATED START condition. ▪ Combined operation can be performed within a transaction, e.g.: START,Command to the slave,REPEATED START,Read from slave,STOP Signals - Sensors  UART (Universal Asynchronous Receiver/Transmitter) ▪ Serial, asynchronous communication method. ▪ Uses 2 lines: TX (Transmit) and RX (Receive). ▪ No clock signal, the devices must recover clock from data signal. ▪ Usually, the devices agree on the data rate (baud rate). ▪ Predefined communication speeds from 300 bps up to ~1Mbit/s. ▪ UART is just the digital side, multiple line coding standards (RS-232, RS- 422, RS-485). ▪ Disadvantages: Slower data transfer rates, does not support multiple devices easily. Signals - Sensors  UART (Universal Asynchronous Receiver/Transmitter) communication ▪ The communication could be simplex, half-duplex or full-duplex. ▪ Communication data element could be between 5 and 9 bits (a single character). ▪ The line is idle when no data is transferring. ▪ Every character starts with a „Start” bit, followed by the data bits. ▪ Error checking is optional: parity bit after data bits. ▪ Character ends with the „Stop” bit. Signals - Sensors  Parity check ▪ Every communication can be distorted by noise or some other communication problem. ▪ For error detection a redundancy must be added. ▪ Parity check is one of the simplest method. ▪ Transmitter counts the number of „1” bits in the transmitted character. ▪ Depending on the parity check method („odd” or „even” parity), adds a parity bit to the end of the character. Signals - Sensors  Odd and even parity ▪ In case of „odd” parity method: ▪ Parity bit will be „1” if the number of „1” is even (make the number odd). ▪ Parity bit will be „0” if the number of „1” is odd (keep the number odd). ▪ In case of „even” parity method: ▪ Parity bit will be „1” if the number of „1” is odd (make the number even). ▪ Parity bit will be „0” if the number of „1” is even (keep the number even). Signals - Sensors  UART communication settings ▪ For UART to work some settings must be the same on both ends: ▪ Line coding voltage level. ▪ Communication speed (bit rate or baud rate). ▪ Number of data bits (5-9). ▪ With parity or without parity. ▪ Number of stop bits (1 or 2). ▪ Flow control. ▪ Most common mode: 8N1 (8 data bits, no parity, 1 stop bit). ▪ UART is widely used for terminal applications (for example: Cisco routers use 9600bps, 8N1 by default). Signals - Sensors UART communication (8N1) Signals - Sensors  1wire interface ▪ Developed by Dallas Semiconductors. ▪ It uses 2 wires: communication line and ground. ▪ Communication line provides the power supply for the slave devices. ▪ Every device connects to the communication wire with an open-drain output with a pull-up resistor, which means every device can pull the wire to the „0” level. ▪ Every device can monitor the state of the wire. ▪ Quite slow (16.3kbit/s, but there is a „burst” mode with 160kbit/s). ▪ It can work via fairly long wires (~100m). Signals - Sensors  1wire interface communication ▪ Wire idle state is „1”. ▪ Master device can initiate the data transfer by pulling the wire to the zero level for at least 480us (this resets all slave devices). ▪ After that, slave devices send a „presence” signal by pulling the wire to the zero level for 60us. Signals - Sensors  1wire interface protocol ▪ If master wants to transmit data, it pull the wire to the zero level: ▪ 1-15us for „1” logical value. ▪ 60us for „0” logical value. ▪ When master reads data, it will send a short pulse (1-15us). ▪ After that, the slave device can pull down the line for value „0” for 60us. ▪ For sending value „1”, the slave will do nothing. ▪ The basic sequence contains a reset pulse, 8 bits of command and a data byte. ▪ Multi slave system is possible, every device has a 64 bit ID. Signals - Sensors 1wire interface timing Signals - Sensors  Universal Serial Bus (USB) ▪ A standardized serial bus system used for communication and power supply between computers and peripherals. ▪ Full-duplex communication, supports multiple speeds (USB 2.0, USB 3.0, etc.). ▪ Can deliver power to connected devices (5V DC, 0.5A or 0.9A). ▪ High-speed data transfer, widely adopted, plug-and-play functionality. ▪ Disadvantages: More complex than SPI, I2C, UART. ▪ Not for IC-IC communication. Signals - Sensors