The Modbus protocol is a communication protocol that enables
devices to use data via a joint connection if the devices communi‐
cate with each other via the "Modbus RTU" Modbus Application
Protocol Specification V1.1b3.
The metering pump gamma/ X GMXa does not emulate every type
of MODICON device.
The "Modbus RTU" specification describes the "data link layer" and
the physical layer.
The notification structure of the function codes uses "Modbus RTU"
standards.
IEEE 32-bit floating point numbers and integers are used.
Default settings
The metering pump gamma/ X GMXa is delivered
to the customer with predetermined settings, with
"Bus address 20" and a baud rate of 19200 baud.
You can change the slave address and the baud
rate in the metering pump gamma/ X, GMXa in the
‘Settings
è
Modbus RTU’ menu (First switch
Modbus to ‘inactive’ ).
Implementation of the Modbus interface is based on the following
standards:
n
www.modbus.org/docs/Modbus_over_serial_line_V1_02.pdf
Additional information about Modbus can be found at
www.modbus.org
or the websites of your country's Modbus organi‐
sation - if available.
3.4.1 "Modbus RTU" message structure
Parameter Value
Standard RS-485
Number of data bits per character 11 bits:
1 start bit
8 data bits
1 parity bit - "even"
1 stop bit
Data rate (Baud) Pre-set: 19200
(9600, 19200, 38400)
Error check CRC-16 (cyclic redundancy check); polynomial =
0x0A001 (1010000000000001
Tab. 27: A telegram comprises:
Component Length
Slave address 1 byte
Function code 1 byte
Supplementary Operating Instructions for Modbus RTU
44
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