SBUS Outputting Solid HIGH on ESP32-C3

[invictus-anic3tus]

Hello!

I've been struggling with an issue for a while now, where the non-inverted SBUS output from my ESP32-C3 XIAO is a solid HIGH, as indicated by a multimeter and by digitalread(). I'm attempting to transmit 16 channels of SBUS data to a flight controller, and I can confirm that the channels are valid and the formatting is good. The non-inverted HIGH output is going through a hardware inverter thus outputting a LOW, which is also functional and multimeter-tested. Here is my code (well, at least a shortened version of it):

#include "sbus.h"

#define SBUS_TX_PIN 5         // sbus pin for communicating with the fc
HardwareSerial SerialSbus(1);  // UART1

// Non-inverted sbus
bfs::SbusTx sbus_tx(&SerialSbus, SBUS_RX_PIN, 4, false);

void setup() {
    Serial.begin(115200);

    SerialSbus.begin(100000, SERIAL_8E2, 4, SBUS_TX_PIN, false);

    // SBUS init
    sbus_tx.Begin();
}

void loop() {
    uint16_t testChannels[16] = {992,992,992,992,992,992,992,992,992,992,992,992,992,992,0,992};  // testing to see if it outputs correctly
    bfs::SbusData test_data;
    memcpy(&test_data, testChannels, sizeof(testChannels));

    // Send sbus packet every 20ms
    sbus_tx.data(test_data);

    // Debug: Print SBUS data before transmission
    Serial.print("Data Channels: ");
    for (int i = 0; i < 16; i++) {
        Serial.print(test_data.ch[i]);
        Serial.print(" ");
    }
    Serial.print("digital read: ");
    Serial.println(digitalRead(SBUS_TX_PIN)); // This is consistently outputting 1, and the multimeter confirms this. Also no SBUS signal seen by my flight controller.

    sbus_tx.Write();
    delay(20);
}

What could be the issue? Thanks! Apologies in advance if I neglected to include any vital information.

[flybrianfly]

I'd doubt that you would be able to see serial data on a multimeter - the switching is just too fast. Same issue using digitalRead, especially with the delay, I would doubt that you would pick up anything. Finally, sometimes doing a digitalRead like that will change the pin behavior so it's no longer a serial line.

I would probably start with a loopback test - looping back the TX to the RX line and using both the transmit and receive classes to make sure that you can read the channel values that you transmit.

[invictus-anic3tus]

Will do, thanks! I'll reply back here with the results later.