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+--- Forum: KC868-A2v3 (https://www.kincony.com/forum/forumdisplay.php?fid=77)
+--- Thread: MODBUS (/showthread.php?tid=9355)
MODBUS - frasanc - 05-25-2026
We have a question about reading Modbus RTU:
With A2:
RS485:
RXD:35
TXD:32
With A2V3:
RS485:
RXD:GPIO15
TXD:GPIO7
With A2 can read, but not with A2V3. Any idea?
// A2v3:
HardwareSerial MBus(1);
MBus.begin(9600, SERIAL_8N1, 15, 7);
pinMode(4, INPUT); // modo auto
// A2:
HardwareSerial MBus(2);
MBus.begin(9600, SERIAL_8N1, 35, 32);
ModbusMaster node;
node.begin(1, MBus);
uint8_t r = node.readInputRegisters(6, 2); // FC04 @ PDU 6
Someone could help us?
RE: MODBUS - admin - 05-25-2026
you can try to exchange RXD and TXD pin.
RE: MODBUS - frasanc - 05-25-2026
![[Image: A2v3-diagram.jpg]](https://www.kincony.com/images/A2v3/A2v3-diagram.jpg)
We use that PIN photo to identify A-B PIN.
// src/modbus_reader.cpp
void ModbusReader::applyUartPins(uint32_t baudRate) {
int8_t rxPin = RS485_RX_PIN; // 15
int8_t txPin = RS485_TX_PIN; // 7
if (s_rs485SwapTxRx) {
rxPin = RS485_TX_PIN; // swap: begin(9600, 8N1, 7, 15)
txPin = RS485_RX_PIN;
}
_serial.begin(baudRate, MODBUS_SERIAL_CFG, rxPin, txPin);
}
```cpp
ModbusResult ModbusReader::readInputRegisters(uint8_t slaveId,
uint16_t startAddress,
uint8_t count) {
flushRxQuiet();
_node.begin(slaveId, _serial);
uint8_t status = _node.readInputRegisters(startAddress, count);
silentBusGapAfterFrame();
// On success: values = _node.getResponseBuffer(i);
}
I put here some examples I'm following, including change pin number according your suggestion but is not working. I don't know if there is som example for that board.
RE: MODBUS - admin - 05-25-2026
here is KC868-A2v3 board RS485 arduino demo code, you can test with it.
https://www.kincony.com/forum/showthread.php?tid=7962
RE: MODBUS - frasanc - 05-26-2026
Thanks for your link...I detect my mistake and now works fine.
RE: MODBUS - admin - 05-26-2026
ok, good.