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+--- Thread: KC868-A16 + 2 × R4DCB08 – CRC errors (/showthread.php?tid=8186)
KC868-A16 + 2 × R4DCB08 – CRC errors - Akash24 - 06-13-2025
Hi KinCony team,
Hardware
• KC868-A16 (ESP32, ESPHome 2025.2.2, UART TX GPIO13 / RX GPIO16, 9600 baud, 8-N-1)
• Two R4DCB08 temperature-collector boards, each with 4-8 × DS18B20 probes
• 24 V DC power supply feeding both collectors
• RS-485 cabling: shielded twisted pair
Address & jumpers
• Board 1 → Modbus ID 0x01, TERM OFF, BIAS OFF
• Board 2 → Modbus ID 0x02, TERM ON (far end), BIAS OFF
• KC868 terminator jumper → ON when only board #1 is present, OFF when both boards are in the chain
Wiring topology
KC868 A/B/GND → short stub to board #1 → 3 m cable → board #2 (terminator)
(I originally had both collectors fanned out from a terminal block; I have now rewired them in strict daisy-chain as shown in the attachment.)
Symptoms
• With only board #1 on the line everything is stable – ESPHome reads register 0x0000 and publishes 23.8 °C.
• As soon as I plug in board #2 I get continuous
csharp
CopyEdit
Code:
[W][modbus:125]: Modbus CRC Check failed!
[W][modbus_controller]: Modbus device=2 set offline• Swapping A/B on both collectors made no difference.
• If I change board #2’s address to 0x01, unplug board #1, it answers correctly, so the hardware itself works.
What I’ve tried
- Checked DIP addresses (01 / 02) – OK
- Verified 5 V on both collectors while polling – 5.05 V
- Tried baud 2400 on both sides – still CRC errors
- Tested with just 30 cm jumpers between boards – same result
Are there any known issues with two R4DCB08 units on the same KC868-A16 RS-485 bus?
Can you suggest further tests (e.g. different termination/bias settings, oscilloscope waveforms to capture) or firmware settings that typically resolve “CRC Check failed” when the wiring looks correct?
Log snippet and wiring photo are attached.
Thanks in advance for any pointers!
RE: KC868-A16 + 2 × R4DCB08 – CRC errors - admin - 06-15-2025
sorry, i don't have this type of sensor. i thnk,, you can test one A16 board with one sensor firstly. when work well, connect with second sensor.