6 Modbus and PNP/NPN conversion
1.Communication specifications
| Item | Content | |
| Communication protocol | Modbus protocol | |
| Standard specifications | Modbus-RTU slave station communication protocol | |
| Maximum connections | 247 | |
| Topological structure | Bus type | |
| Slave station function | Number of messages that can be received and requested at the same time | 1 |
2. Hardware configuration
| Terminal identification | Terminal name | Function description | Jumper/dialing position |
| J5 | 485 communication terminal resistance setting jumper | Match terminal resistance |
|
Modbus communication port of this product is located on the control panel, as shown in the following figure:
RS485 Connection Topology
RS485 bus connection topology is shown in the following figure. 485 bus is recommended to use shielded twisted pair (STP), 485+, 485-: Adopt twisted pair to connect; Only 120 Ω terminal matching resistors are connected at both ends of the bus to prevent signal reflection; All node 485 signal grounds are connected together; Connect 128 nodes at most, and the distance between branches of each node should be less than 3m.
Multi-node connection mode
When the number of nodes is large, 485 bus must be daisy chain connection. If branch connection is needed, the branch length from bus to node had better be short. It is recommended that it should not exceed 3m. Star connection should be forbidden. The diagram of common bus structure is as follows:
Figure1 Daisy chain connection
Figure2 Branch connection
Figure3 Star connection (Forbidden)
Transmission distance
The maximum number of nodes and transmission distance supported by our standard RS485 circuit at different rates are shown in the following table.
| Transmission distance (m) | Rate (kbps) | Number of nodes | Wire diameter |
| 100 | 115.2 | 128 | AWG26 |
| 1000 | 19.2 | 128 | AWG26 |