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5
Functional description
Page 94
gas-lab
Q1
Communication
protocol
:
Based on Modbus RTU/Modbus ASCII according to the
Modicon
Modbus Protocol Specification
(Jan. 1991, MODICON Inc.), point-
to-point
Interface:
V24 (RS232) with PC/AT pin assignment at the
gas-net
device
(COM2-interface).
RS232, RS422 or RS485 via serial interface of an MSER2-board
in the
gas-net
device.
Transmission rate:
adjustable to 2400, 9600, 19200 or 38400 baud
Transmission
parameters:
Modbus RTU 8 data bits, Modbus ASCII 7 data bits
even parity, 1 stop bit pre-allocated
Modbus telegrams:
Maximum of 250 bytes (125 register words) per telegram.
Only the Modbus telegram types 03 and 16 are supported.
Modbus response
telegrams:
In the gateway = slave operating mode, the gateway generates
the response telegrams listed in the table below when an error
occurs:
Error
number
Modbus error
designation
Cause of the error
01
illegal function
The telegram type received is not permissible, i.e. it is
neither of the 03 nor of the 16 telegram type.
Only Modbus telegram types with the functional
numbers 03 (= read holding registers) or 16 (= preset
multiple registers) are needed in the gateway; this is
why only these are supported.
02
illegal data address
The indicated data address is not permissible.
04
failure in associated
device
Other