Modbus Communication; Electrical Specification; Outer Protocol; Repeaters - rotork Modbus IQ Pro Technical Manual

6 MODBUS COMMUNICATION

6.1 Electrical Specification

Line Electrical Specification:

6.2 Outer Protocol

Modbus Transmission Mode
Supported Baud Rates
Number of bits per character
Start bits
Data bits (LSB first)
Parity (configurable)
Stop bits (configurable)
Error checking
Message turn round time/delay time
Minimum period between request and response:
Data Speed
300
(Baud)
Turn Round
188
Time (ms)
Repeater
NA
Delay (μs)
Note:  – In the Single Highway with Internal Repeater Modbus Module option there is a
propagation delay in the repeater.
 – NA = not applicable, the repeater function cannot be used below 2,400 baud.
Maximum period between request and response: 190 ms.

6.3 Repeaters

A single segment supports up to 32 nodes, one of which is usually the PLC. The addition of repeaters
allows the segment to be extended in length or increase the number of nodes connected or both. The
maximum lengths at different speeds are discussed in Section 4.2. The number of repeaters in a
single highway should be kept to a minimum, as this can seriously extend the delay between a
message being sent and the response arriving at the PLC.
The Single highway with Inbuilt Isolating Repeater version of the Modbus Module introduces
propagation delays as mentioned above. Care must be taken in any system design to allow for these
delays.
RS-485, two-wire, half duplex
RTU (8 bit Binary data)
300, 600, 1k2, 2k4, 4k8, 9k6, 19k2, 38k4, 57k6, 115k2
(2k4, 4k8, 9k6, 19k2, 38k4, 57k6, 115k2 when using the
internal repeater option)
1
8
Odd, Even, None
1 or 2
CRC
600 1k2 2k4
100 60 40
NA NA 3.5
Publication PUB091-003-00_0119
4k8 9k6 19k2
28 24 20
3.5 3.5 3.5
Modbus Communication
38k4 57k6 115k2
20 20 20
3.5 3.5 3.5
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