Niagara R2 Modbus Driver Support for 6-Digit Address Format

[Product_Support]

Issue

Does the Niagara R2 Modbus driver support a 6-digit address format?

Product Line

TAC IA Series

Environment

Niagara R2 Modbus driver

Cause

The Modbus protocol uses different notations for register addressing. The 6-digit format (e.g., 400001–409999) is a convention that shifts the type digit one position to the left to represent more registers. Niagara R2 does not support this convention when using Modbus-formatted addresses.

Resolution

• The 6-digit Modbus notation is not supported in Niagara R2 when using Modbus format in the driver.
• However, you can use decimal or hexadecimal notation to specify addresses beyond the 5-digit range.
• When using Modbus format:
  • The leftmost digit (e.g., '4' for holding registers) indicates the point type.
  • The driver subtracts 1 from the entered address because Modbus uses base-1 indexing, while decimal uses base-0.

Example Conversion

To read data from register 422202:

1. Drop the leading digit → 22202
2. Subtract 1 → Decimal address 22201
3. Optionally convert to hex → 56B9

Key Notes:

• First 1,000 holding registers:
  • Modbus notation: 40001–49999
  • Decimal: 0–9998
  • Hex: 0–270E
• There are 64,000 holding registers available, but Modbus format limits notation to 5 digits.