IBM Modbus Plus manual Data Types and Lengths

Modbus Plus X-Link Driver User’s Guide

4.1 Data Types and Lengths

The Modbus Plus Driver supports three X-Link data formats; Bits and Integers, as well as Floats.

The Modbus Plus protocol does not support floating point. The driver will truncate any floating point numbers before transmission, and expand the integer numbers to floating point after retrieval when floating points are requested.

The type of Modbus Plus command that the driver generates depends on the address type specified.

The length of the data portion in a command is constrained by the Modbus Plus protocol. Mappings that are configured with the X-Link reading or writing the data on the Modbus Plus network should be restricted to a maximum size of:

Data Type	X-Link Access	Maximum Size (bytes)
COIL	Read	250
COIL	Write	100
Registers	Read	250
Registers	Write	200
Global Data	Read/Write	64

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