Basic Modbus Register 201: Inlet fan speed

Technical Definition

The register Inlet fan speed at address 201 is used to monitor inlet fan speed on the Basic.

• Protocol: Modbus RTU
• Data Type: INT16
• Unit: %
• Access: Read Only

How to Read (Python pymodbus)

Use this code snippet to read this specific value via RS485:

from pymodbus.client.sync import ModbusSerialClient

client = ModbusSerialClient(method='rtu', port='/dev/ttyUSB0', baudrate=9600)
client.connect()

# Read Inlet fan speed (Address: 201)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=201, count=2, unit=1)

if not result.isError():
    print(f"Raw Value: {result.registers}")
else:
    print("Error reading register")

client.close()

Integration (Home Assistant)

Paste this into your configuration.yaml:

- platform: modbus_controller
  name: "Inlet fan speed"
  address: 201
  value_type: INT16
  unit_of_measurement: "%"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

graph TD
    PLC[Host Controller / Home Assistant]
    Device[Basic]

    PLC -- "A+ (D+)" --> Device
    PLC -- "B- (D-)" --> Device
    PLC -- GND --> Device

💡 Engineer's Insight

Analysis: Speed of the inlet fan, likely in RPM or percentage. Indicates fresh air intake.

Troubleshooting: 0 could indicate fan motor failure, power interruption, control signal absence, or a blocked inlet.