Micro:bit multiple "serial on data recieved" don't work properly (only the last one works)

martinwork · May 9, 2026, 7:23pm

Yes, I think you’re right. Looking at the code, each handler block overwrites the same delimiter string, and the same pointer to the event’s handler.

It’s the same for Bluetooth UART: https://forum.makecode.com/t/bluetooth-uart-command-to-move-servo-only-work-in-one-direction/29202

github.com/microsoft/pxt-microbit

libs/core/serial.cpp

master


      
            if (n == 0) return mkString("", 0);
            return PSTR(uBit.serial.read(n, MicroBitSerialMode::ASYNC));
          }
          
          /**
          * Register an event to be fired when one of the delimiter is matched.
          * @param delimiters the characters to match received characters against.
          */
          //% help=serial/on-data-received
          //% weight=18 blockId=serial_on_data_received block="serial|on data received %delimiters=serial_delimiter_conv"
          void onDataReceived(String delimiters, Action body) {
            uBit.serial.eventOn(MSTR(delimiters));
            registerWithDal(MICROBIT_ID_SERIAL, MICROBIT_SERIAL_EVT_DELIM_MATCH, body);
            // lazy initialization of serial buffers
            uBit.serial.read(MicroBitSerialMode::ASYNC);
          }
          
          /**
           * Send a piece of text through the serial connection.
           */
          //% help=serial/write-string

https://github.com/microbit-foundation/codal-core/blob/master/source/driver-models/Serial.cpp#L932

github.com/microsoft/pxt-common-packages

libs/base/core.cpp

master


      
                      return p;
                  }
              }
              return 0;
          }
          
          HandlerBinding *findBinding(int source, int value) {
              return nextBinding(handlerBindings, source, value);
          }
          
          void setBinding(int source, int value, Action act) {
              HandlerBinding *curr = NULL;
              for (auto p = handlerBindings; p; p = p->next) {
                  if ((p->source == source) && (p->value == value)) {
                      curr = p;
                      break;
                  }
              }
              if (curr) {
                  curr->action = act;
                  return;

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Micro:bit multiple "serial on data recieved" don't work properly (only the last one works)

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