Distributed Real- Time Control Systems

Transcription

1 Distributed Real- Time Control Systems Lecture 4 Embedded Systems Communica:ons A. Bernardino, C. Silvestre, IST- ACSDC 1

2 Interfaces I/O Digital I/O Analog Input PWM Serial SPI TWI A. Bernardino, C. Silvestre, IST- ACSDC 2

3 Asynchronous Serial Communica:ons The asyncrononous serial communica:ons protocol allows to communicate with a wide range of devices: Dial- up modems. Computer mouse and keyboards GPS devices LCDs MIDI etc Simple and cost effec:ve. No clock is required and the data link can be reduced to three wires (RX, TX, GND). Electrical implementa:ons: Raw (TTL) RS232- C (PC serial) RS485 - Twisted cable, current signaling, large distances. A. Bernardino, C. Silvestre, IST- ACSDC 3

4 Transmission Protocol Frame structure Configura:ons Full or half- duplex Number of bits per character (5-9) Order in which bits are sent (endianness) Bits per second ( K ) Parity (Odd, Even, None) Number of stop bits (1-2) A. Bernardino, C. Silvestre, IST- ACSDC 4

5 ATMEL 328 USART USART connected to pins 0 (Rx) and 1 (Tx). Full Duplex Opera:on (Independent Serial Receive and Transmit Registers) Asynchronous or Synchronous Opera:on Master or Slave Clocked Synchronous Opera:on High Resolu:on Baud Rate Generator Supports Serial Frames with 5, 6, 7, 8, or 9 Data Bits and 1 or 2 Stop Bits Odd or Even Parity Genera:on and Parity Check Supported by Hardware Data OverRun Detec:on Framing Error Detec:on Noise Filtering Includes False Start Bit Detec:on and Digital Low Pass Filter Three Separate Interrupts on TX Complete, TX Data Register Empty and RX Complete Mul:- processor Communica:on Mode Double Speed Asynchronous Communica:on Mode A. Bernardino, C. Silvestre, IST- ACSDC 5

6 Example: Reading RFID tags RFID Tags are small devices that transmit data wirelessly and without contact from a tag adached to an object. They can be passive, responding when subject to an electromagne:c field, or ac:ve, powered with small bateries. They are used for mul:ple purposes: Tracking goods Access control Automa:c payment Passports and ID documents A. Bernardino, C. Silvestre, IST- ACSDC 6

7 Example: Reading RFID tags A tag consists of a start character followed by a 10- digit tag and is terminated by an end character. Example: Parallax RFID reader: const int startbyte = 10; const int endbyte = 13; const int taglength = 10; const int totallength = taglength + 2; char tag[taglength + 1]; int bytesread = 0; void setup() { Serial.begin(2400); // set to the baud rate of your RFID reader pinmode(2,output); // connected to the RFID ENABLE pin digitalwrite(2, LOW); // enable the RFID reader void loop() { if(serial.available() >= totallength) // check if enough data { if(serial.read() == startbyte) { bytesread = 0; // start of tag so reset count to 0 while(bytesread < taglength) // read 10 digit code { int val = Serial.read(); if((val == startbyte) (val == endbyte)) // end of code break; tag[bytesread] = val; bytesread = bytesread + 1; // ready to read next digit if( Serial.read() == endbyte) // check end character { tag[bytesread] = 0; // terminate the string Serial.print("RFID tag is: "); Serial.println(tag); A. Bernardino, C. Silvestre, IST- ACSDC 7

8 Example: Playing MIDI MIDI allows mul:ple instruments to be played from a single controller. const byte notes[8] = {60, 62, 64, 65, 67, 69, 71, 72; const int length = 8; const int switchpin = 2; void setup() { Serial.begin(31250); pinmode(switchpin, INPUT); digitalwrite(switchpin, HIGH); void loop() { if (digitalread(switchpin == LOW)) { for (byte notenumber = 0; notenumber < 8; notenumber++) { playmidinote(1, notes[notenumber], 127); delay(70); playmidinote(1, notes[notenumber], 0); //MUTE delay(30); void playmidinote(byte channel, byte note, byte velocity) { byte midimessage= 0x90 + (channel - 1); //play on channel 1 Serial.write(midiMessage); Serial.write(note); Serial.write(velocity); //volume A. Bernardino, C. Silvestre, IST- ACSDC 8

9 Soqware Serial Ports To use mul:ple serial devices (e.g. to communicate with a serial device and the host computer), Soqware serial ports can be used. Soqware serial ports are regular I/O ports that implement the serial protocol in Soqware. Use library SoqwareSerial A. Bernardino, C. Silvestre, IST- ACSDC 9

10 Example: Serial LCD #include <SoqwareSerial.h> const int rxpin = 2; // pin used to receive (not used) const int txpin = 3; // pin used to send to LCD SoqwareSerial serial_lcd(rxpin, txpin); // on pins 2 and 3 void setup() { Serial.begin(9600); // 9600 baud for the built- in serial port serial_lcd.begin(9600); //soqware serial port also for 9600 int number = 0; void loop() { serial_lcd.print("the number is "); // send text to the LCD serial_lcd.println(number); // print the number on the LCD Serial.print("The number is "); Serial.println(number); // print the number on the PC console delay(500); // delay half second between numbers number++; // to the next number A. Bernardino, C. Silvestre, IST- ACSDC 10

11 I2C and SPI Busses I2C Inter- Integrated Circuit Also known as TWI (two wire interface) Two wires (clock+data), half- duplex, require pull- ups, for low- data rate devices (sensors) Level Triggered Use Acknowledge Reduced Noise Immunity SPI Serial Peripheral Interface Also Known as SSI (syncronous serial interface). SPI Full- duplex, for high- data raterequirements (e.g. ethernet). Edge Triggered No Acknowledge Good Noise Immunity A. Bernardino, C. Silvestre, IST- ACSDC 11

12 I2C Connec:ons Only one master (typicaly the arduino), mul:ple slaves. Each slave must have a unique address (7 bit typ.). SCL Serial control line SDA Serial data line A. Bernardino, C. Silvestre, IST- ACSDC 12

13 I2C Timing Diagram A. Bernardino, C. Silvestre, IST- ACSDC 13

14 I2C Protocol A. Bernardino, C. Silvestre, IST- ACSDC 14

15 SPI Connec:ons Use slave select lines. Do not require pull- ups. SCLK - serial clock (output from master); MOSI: master output, slave input (output from master); MISO: master input, slave output (output from slave); SS: slave select (ac:ve low, output from master). A. Bernardino, C. Silvestre, IST- ACSDC 15

16 SPI Timing Diagram A. Bernardino, C. Silvestre, IST- ACSDC 16

17 Using the Wii Nunchunk The Wii Nunchunk uses I2C bus. Uses Wire Library. Nunchunk: No datasheet but was reverse engineered. #include <Wire.h> // ini:alize wire const int vccpin = A3; // +v provided by pin 17 const int gndpin = A2; // gnd provided by pin 16 const int datalength = 6; // number of bytes to request sta:c byte rawdata[datalength]; // array to store nunchuck data enum nunchuckitems { joyx, joyy, accelx, accely, accelz, btnz, btnc ; void setup() { pinmode(gndpin, OUTPUT); // set power pins pinmode(vccpin, OUTPUT); digitalwrite(gndpin, LOW); digitalwrite(vccpin, HIGH); delay(100); // wait for things to stabilize Serial.begin(9600); nunchuckinit(); void nunchuckinit(){ Wire.begin(); // join i2c bus as master Wire.beginTransmission(0x52);// transmit to device 0x52 Wire.write((byte)0x40); // sends memory address Wire.write((byte)0x00); // sends sent a zero. Wire.endTransmission(); // stop transmiwng A. Bernardino, C. Silvestre, IST- ACSDC 17

18 Using the Wii Nunchunk (cont) void loop(){ nunchuckread(); int accelera:on = getvalue(accelx); if((accelera:on >= 75) && (accelera:on <= 185)) { //map returns a value from 0 to 63 for values from 75 to 185 byte x = map(accelera:on, 75, 185, 0, 63); Serial.write(x); delay(20); // the :me in milliseconds between redraws boolean nunchuckread(){ int cnt=0; Wire.requestFrom (0x52, datalength); // request data while (Wire.available ()) { rawdata[cnt] = nunchuckdecode(wire.read()); cnt++; nunchuckrequest(); // send request for next data payload if (cnt >= datalength) return true; // if all 6 bytes received else return false; //failure int getvalue(int item){ if (item <= accelz) return (int)rawdata[item]; else if (item == btnz) return bitread(rawdata[5], 0)? 0: 1; else if (item == btnc) return bitread(rawdata[5], 1)? 0: 1; // Encode data to format that most wiimote drivers accept sta:c char nunchuckdecode (byte x) { return (x ^ 0x17) + 0x17; // Send a request for data to the nunchuck sta:c void nunchuckrequest(){ Wire.beginTransmission(0x52);// transmit to device 0x52 Wire.write((byte)0x00); // sends one byte Wire.endTransmission(); // stop transmiwng A. Bernardino, C. Silvestre, IST- ACSDC 18

19 Driving 7- Segment Displays The MAX7221 A. Bernardino, C. Silvestre, IST- ACSDC 19

20 Driving 7- Segment Displays #include <SPI.h> const int slaveselect = 10; // pin used to enable the ac:ve slave const int numberofdigits = 2; // change to match desired const int maxcount = 99; int count = 0; void setup() { SPI.begin(); // ini:alize SPI pinmode(slaveselect, OUTPUT); digitalwrite(slaveselect,low); // select slave // prepare the 7221 to display 7- segment data - see data sheet sendcommand(12,1); // normal mode (default is shutdown) sendcommand(15,0); // Display test off sendcommand(10,8); // set medium intensity (range is 0-15) sendcommand(11,numberofdigits); // 7221 digit scan limit sendcommand(9,255); // use standard 7- segment digits digitalwrite(slaveselect,high); // deselect slave void loop() { displaynumber(count); count = count + 1; if (count > maxcount) count = 0; delay(100); // func:on to display up to four digits on a 7- segment display void displaynumber( int number) { for (int i = 0; i < numberofdigits; i++) { byte character = number % 10; // rightmost decade // send digit number as command, first digit is command 1 sendcommand(numberofdigits- i, character); number = number / 10; void sendcommand( int command, int value) { digitalwrite(slaveselect,low); // chip select is ac:ve low // 2 byte data transfer to the 7221 SPI.transfer(command); SPI.transfer(value); digitalwrite(slaveselect,high); // release chip, signal end A. Bernardino, C. Silvestre, IST- ACSDC 20

21 Other I2C and SPI devices Port Expanders Digital Thermometers External Real- Time Clocks External EEPROM 7- Segment leds LED drivers Mul:plexers ADC, DAC Pressure Sensors Ethernet controllers CAN controllers UART Digital Poten:ometers Flash Memories Touch screen controllers Audio Mixers Sample Rate Converters A. Bernardino, C. Silvestre, IST- ACSDC 21

22 Connect Two Arduinos with I2C Master- Slave A. Bernardino, C. Silvestre, IST- ACSDC 22

23 The Master The master sends characters received on the serial port to an Arduino slave using I2C. #include <Wire.h> const int address = 4; // the address to be used by the communica:ng devices void setup() { Wire.begin(); void loop() { char c; if(serial.available() > 0 ) { // send the data Wire.beginTransmission(address); // transmit to device Wire.write(c); Wire.endTransmission(); A. Bernardino, C. Silvestre, IST- ACSDC 23

24 The Slave The slave prints characters received over I2C to its serial port: #include <Wire.h> const int address = 4; // the address to be used by the communica:ng devices void setup() { Serial.begin(9600); Wire.begin(address); // join I2C bus using this address Wire.onReceive(receiveEvent); // register event to handle requests void loop() { // nothing here, all the work is done in receiveevent void receiveevent(int howmany) { while(wire.available() > 0) { char c = Wire.read(); // receive byte as a character Serial.write(c); // echo A. Bernardino, C. Silvestre, IST- ACSDC 24