Modbus Functions | FP Web-Server V2.11 |
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12.3 Modbus-TCP Client of the FP Web-Servers in General
Either the PLC or a Modbus-RTU master unit can control the Modbus-TCP client functions of the FP Web-Server.
•For PLC control a shared buffer in the PLC's memory is used. The PLC program places the server IP address and Modbus commands in this buffer. The FP Web-Server reads the buffer and executes the commands. Additionally, the PLC can also access a Modbus-RTU slave unit via the 9-pin RS232C interface.
•Any Modbus-RTU master connected to the 9-pin RS232C of the FP Web-Server can access a remote Modbus-TCP server. This gateway routes all Modbus-RTU function requests to the Modbus-TCP server. Optionally the Modbus-RTU master can address different Modbus-TCP servers (IP address and/or unit ID is calculated by the accessed RTU slave address) or the local PLC directly.
The Modbus-TCP communication can also be done via modem. For this the client (FP Web-Server controlled by the PLC, see PLC sample program "Dialup-StayOnline.asc") has to dial up the Modbus-TCP server to establish a modem connection before Modbus-TCP communication can take place.
The PLC can also control continuous, automatic data exchange via Modbus protocol. See PLC sample program "Modbus-TCP-Client.asc", which is installed along with the FP Web-Configurator.
Features:
•This function uses the configurable Modbus-to-PLC address translation table.
•The gateway routes all Modbus function requests.
•The Modbus-TCP client can also handle UDP broadcast messages (all responses from the servers are ignored).
•An integrated setup wizard helps you to configure the Modbus-TCP client.
•NumberMaxOfClientTransactions = 6 (if all are busy, then the oldest is disconnected).
•SO-RCVBUF, SO-SNDBUF = 4kB with TCP and 2kB with UDP (other IP Stack parameters can be defined).