4.2.5 RS-485 (Modbus RTU)

RS-485 Test Area

The Test tab is designed for diagnostics and manual communication with Modbus devices.

Single Request

• Enter a one-line configuration string (same format as in the main panel):

SensorName,1,0x0100,temp,4,1.0,0,ABCD

• Sends Function 0x03 to slave ID 1
• Reads 2 registers (4 bytes)
• Applies byte order, scaling, and offset
• Displays both raw and interpreted results

Response Breakdown

When a Single Request is executed in the Test tab, the SmartSampler shows a detailed breakdown of the received Modbus response.

• The raw byte buffer is displayed exactly as returned by the sensor.
• All four possible byte orders (ABCD, DCBA, BADC, CDAB) are decoded and shown for comparison.
• The configured offset and scaling values are applied in every case.
• This helps you quickly determine if the selected byte order matches the sensor datasheet and expected values.
• The Final Result highlights the value calculated using the current Single Request configuration (address, register, scaling, offset, order).

Example response to: Read 4 bytes at register 0x0100 from address 1

Raw buffer: 85 12 cd 41
order ABCD = 25.634
order DCBA = -0.000
order BADC = -202920224.000
order CDAB = 0.000
Raw float = 25.634
Final Result = temp: 25.63

This structured output allows you to verify:

• That the sensor is returning valid data.
• Which byte order produces meaningful values.
• Whether the configured offset and scaling match expectations.

Debug Passthrough

• Passthrough mode forwards Modbus traffic directly, without parsing.
• Useful for:
  • Testing sensors with custom tools
  • Sniffing communication
  • Low-level troubleshooting