Modbus Rtu Message Format; Modbus Rtu Function Codes - Honeywell UDC2800 Product Manual

Chapter 12 - Standard Modbus Read, Write and Override Parameters

Modbus RTU Message Format

Table 12-1: Modbus RTU Message Formats
Coding system
Number of data bits per character
Parity
Bit transfer rate
Duplex
Error checking
Polynomial
Bit transfer order
End of message

Modbus RTU Function Codes

209
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.
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.
8 bit binary
10 Bits
start bits - 1
data bits - 8
parity bits - 0
stop bits - 1
Not used
300, 600, 1200, 2400, 4800, 9600, 19200,
38400 Selectable
NOTE: Not all instruments support all Baud
Rates.
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).