Connect CPU224, Op3 and other RS485 device

[mrMal]

Hi guys, I am starting a project in which I intend to use a Siemens CPU224 as the main controller and an text_based display_OP3 as the dispalying terminal. To gather process data the CPU224 needs to take the information from some devices which all have RS485 communication port and exchange data via Modbus protocol. Can anbody tell me the hardwareand software sollution for my project ( which Siemens tool, what hardware module or converter should I need to equip, ...) All the advices will be highly appreciated. Regard

[Crossbow]

There is an additional instruction library for the S7-200 which can be purchased, and adds Modbus commands as well as some others. You could then use the RS485 serial port on the front of the CPU. I don't remember them having an additonal serial port module for those units. If you look at the 224XP (newer unit) it has built in analog I/O and 2 serial ports, perhaps that would help you.

[mrMal]

Hello Cross bow I know in S7-200 series of Siemens, the CPU224XP and CPU226 both have two RS485 serial ports and Siemens also have additional Profibus and Ethernet modules for industrial network connection. But here, because of the limitation of budget I would like to use only the normal CPU224 which has only one RS485 port and use no more additional communication module for RS485 devices. I agree with you that I must purchase the add-on Modbus libarary from Siemens in order to talk to RS485 devices via Modbus protocol. But the inquiry here is whether I can use only one RS485 port of CPU224 to communicate with OP3 and RS485 devices or I need to dedicate a separate port only for those RS485 devices. Theoretically I guess it would be possible because there could be 32 devices connected to RS485 network and they can talk with each other. But OP3 and CPU224 use a Siemens-specific protocol other than Modbus protocol therefore I am not sure whether it has some conflicts on this RS485 network.

[Crossbow]

You can't have one RS485 port talk both Modbus and the OP protocol (PPI?). One protocol per port. You will need two ports to accomplish this unless the OP can be set for Modbus.