Network Communication
Each device must have a unique ModBus address for startup and it must be set before connection to the network. The local
DIP switch is used to set the ModBus device address (1-255). Set the device address as shown in Figure 8.
The factory default network configuration is:
Baud Rate
38400
Parity
None
Stop Bits
1
CRC
A001 (CRC-16 reverse)
Delay
0
(minimum)
Note that the ModBus network configuration may be customized at the factory if required. For example, the baud rate and
other parameters may be factory configured to suit specific applications.
The RH/T Sensor operates as a slave. It will not communicate unless a master is connected to the network and sends a request
for information, then the slave will answer. If the device does not communicate properly, first check that the communication
wires are not reversed. Then check that the slave address has a unique setting for the network segment it is connected to.
Finally, verify that the device baud rate, parity bit, stop bit and RTU mode CRC polynomial are correct for the network it is
connected to.
ModBus Protocol
This section describes the implementation of the ModBus protocol. It is intended to assist control system programmers who
may need to add support to their systems to communicate with this device. This device communicates on standard ModBus
networks using RTU mode transmission. It operates as a slave device (address from 1 to 255) and expects a ModBus master
device to transmit queries, which it will answer.
Figure 8
OFF
ON
Greystone Energy Systems, Inc. 150 English Drive, Moncton, NB E1E 4G7 Canada Tel: +1-506-853-3057 Tollfree (North America): +1-800-561-5611 Fax: +1-506-853-6014
Email: [email protected] Web: www.greystoneenergy.com
DIP Switch Position
128
64
32
16
8
4
2
1
ModBus
Address
OFF
OFF
OFF
OFF
OFF
OFF
OFF
ON
1
OFF
OFF
OFF
OFF
OFF
OFF
ON
OFF
2
OFF
OFF
OFF
OFF
OFF
OFF
ON
ON
3
OFF
OFF
OFF
OFF
OFF
ON
OFF
OFF
4
↓
↓
↓
↓
↓
↓
↓
↓
↓
ON
ON
ON
ON
ON
ON
ON
OFF
254
ON
ON
ON
ON
ON
ON
ON
ON
255
2
4
16
32
1
8
64
BUS ADDRESS
128
RTU Message Format
ModB us Framing
8 bit binary
Data Bits
start bits --- 1
data bits --- 8
parity bits --- none
stop bits --- 1
Baud Rate
38400
Duplex
Half duplex
Error Checking
Cyclical Redundancy Check (CRC)
CRC -16 Reversed --- polynomial x16+x15+x2+x0 (0xA001)
Latency
More than 3.5 characters --- minimum
RTU Framing Support and Bit Sequences
Start
1
2
3
4
5
6
7
8
Stop
