Modbus Rtu Serial Communication Port; Overview; Modbus Rtu Message Format; Table 4-1 Modbus Rtu Message Formats - Honeywell UDA2182 User Manual

Modbus RTU Serial Communication Port

4. Modbus RTU Serial Communication Port

4.1 Overview

The Modbus RTU implementation is designed to provide a popular data exchange format connecting the UDA to
both Honeywell and foreign master devices via the optional serial communication port. Modbus RTU allows the
instrument to be a citizen on a data link shared with other devices, which subscribe to the Modicon Modbus
Protocol Reference Guide PI-MBUS-300 Rev. G specification.
The UDA does not emulate any MODICON type device. The Modbus RTU specification is respected in the
physical and data link layers. The message structure of the Modbus RTU function codes is employed and standard
IEEE 32-bit floating point and integer formats are used. Data register mapping is unique to the UDA. Sections 10
and 11 describe the parameter mapping for the UDA.

4.2 Modbus RTU Message Format

Coding system
Number of data bits per
character
Parity
Bit transfer rate
Duplex
Error checking
Polynomial
Bit transfer order
End of message
10

Table 4-1 Modbus RTU Message Formats

8 bit binary
10 Bits
start bits – 1
data bits – 8
stop bits – 1
None
2400, 4800, 9600, 19200, 38400, 57600, 115200 Selectable
Half duplex Transceiver or TX/RX
CRC (cyclic redundancy check)
(CRC-16 10100000000001)
LSB first
Idle line for 3.5 or more characters (>1.82 msec for 19200).
UDA2182 Communications User Guide January 09