Honeywell UDC2800 User Manual

Modbus RTU Message Format
For more information, see "Modbus RTU Message Format" of 51-52-
25-66 Modbus RTU Serial Communications User Manual, which is
available at Honeywellprocess.com.
Table 12-1: Modbus RTU Message Formats
Coding system
8 bit binary
Number of data bits per character
10 Bits
start bits - 1
data bits - 8
parity bits - 0
stop bits - 1
Parity
Not used
Bit transfer rate
300, 600, 1200, 2400, 4800, 9600, 19200,
38400 Selectable
NOTE: Not all instruments support all Baud
Rates.
Duplex
Half duplex Transceiver or TX/RX
Error checking
CRC (cyclic redundancy check)
Polynomial
(CRC-16 10100000000001)
Bit transfer order
LSB first
End of message
Idle line for 3.5 or more characters (>1.82
msec for 19200).
Modbus RTU Function Codes
The Honeywell Universal Modbus RTU protocol uses a subset of the
standard Modbus RTU function codes to provide access to process-
related information. Several MODICON function codes are employed.
It is appropriate to define instrument-specific "user-defined" function
codes. Several standard Modbus RTU function codes are supported.
These standard function codes provide basic support for IEEE 32-bit
floating point numbers and 16-bit integer register representation of
instrument's process data.
Repolling of data is not supported by these instruments.
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Chapter 12 - Standard Modbus Read, Write and Override Parameters

Honeywell UDC2800 Specifications

General

Control Modes	PID, ON/OFF, Manual
Mounting	Panel Mount
Display	Dual 4-digit LED
Input Types	Thermocouple, RTD, mA, mV, V
Output Types	Relay
Power Supply	100-240 VAC, 50/60 Hz
Communication	RS-485 Modbus RTU
Enclosure Rating	NEMA 4X