Matura: Systemtechnik

UART - Universal Asynchronous Receiver / Transmitter

Aufbau	Bitversand

• Austausch von seriellen Daten zwischen zwei Geräten
• Zwei Drähte zwischen Sender und Empfänger, um in beiden Richtungen zu senden und zu empfangen
• Fünf bis maximal neun Datenbits
• Kommunikation:
  • Simplex-Betrieb: die Daten werden nur in eine Richtung gesendet
  • Halbduplex-Betrieb: jede Seite sendet, aber nicht zur selben Zeit
  • Vollduplex-Betrieb: beide Seiten können gleichzeitig senden
• Arbeitet asynchron - kein gemeinsames Taktsignal, daher:
  • Startbit signalisiert das Senden von Nutzdatenbits
  • Stoppbit kennzeichnet das Ende der Nutzdaten
  • Versand von Nutzdaten: normalerweise mit dem niedrigstwertigen Bit zuerst (Least Significant Bit, LSB)

Quelle: https://www.rohde-schwarz.com/at/produkte/messtechnik/oszilloskope/educational-content/uart-verstehen_254524.html

Code

Write

void writeSerialByte(byte value) {
  softSerial.write(value);
}

void writeSerialInt(int value) {
  softSerial.write((value >> 8) & 0xFF); // send the high byte of the LDR value
  softSerial.write(value & 0xFF);  // send low byte of LDR value to master second
}

Request

boolean requestSerialByte(byte command, byte *value) {
  boolean success = false;
  softSerial.write(command);        // send read switch request READ_SWITCH to slave
  delay(COMM_WRITE_READ_DELAY);             // give slave time to accomplish work
  success = softSerial.available() >= 1;
  if (success) {                // slave may send less than requested
    *value = softSerial.read();                 // receive 1 byte from slave
  }
  return success;
}

boolean requestSerialInt(byte command, int *value) {
  boolean success = false;
  byte received[2];
  softSerial.write(command);       // send read switch request READ_LDR to slave
  delay(COMM_WRITE_READ_DELAY);   // give slave time to accomplish work (1 not enough)
  success = softSerial.available() >= 2;
  if (success) {              // slave may send less than requested
    received[0] = softSerial.read();  // receive MSB byte of LDR value from slave
    received[1] = softSerial.read();  // receive LSB byte of LDR value from slave
    *value = received[0] * 256 + received[1]; // build int from 2 bytes
    Serial.print(F("Master: LDR: "));
    Serial.print('('); Serial.print(received[0]);
    Serial.print(' '); Serial.print(received[1]);
    Serial.print(") ");
  }
  return success;
}

Read

boolean readSerialInt(int *value) {
  boolean success = false;
  byte received[2];
  delay(2);                   // give slave time to accomplish work (1 is not enough)
  success = softSerial.available() >= 2;
  if (success) {              // slave may send less than requested
    received[0] = softSerial.read();                 // receive MSB byte of LDR value from slave
    received[1] = softSerial.read();                 // receive LSB byte of LDR value from slave
    *value = received[0] * 256 + received[1]; // build int from 2 bytes
    Serial.print(F("Master: LDR: "));
    Serial.print('('); Serial.print(received[0]);
    Serial.print(' '); Serial.print(received[1]);
    Serial.print(") ");
  }
  return success;
}