NINO_ELC

Dear Emil, the feature in Profibus looks like with what is required for Modbus. Could you implement the same feature for Modbus too? "Define in the Slave the area which is accessible by the Master", and if the Master attempts to Write in this area an error coded reply will be transmitted back. Although I believe that what is needed is a new SCANEX fb, as Joe Tauser has mentioned in his post, which seems not so difficult. I totally agree with Walkerok and Joe comments (+1 , +1 on both guys comments by me too). Anybody have worked with remote I/O modules or other industrial equipments like Drives, Meters, Indicators etc. have met the situation of wrong addressing commands. This feature is provided build even in products costing 45 Euro (panel indicator), which is about the cost of the extra serial port in the Unitronics PLC, but the PLC is not just a dummy indicator. PLC is included in the system to perform the control of it. Leaving a "back door" open, providing access to the control logic can be a disaster.

It is a project we are developing now, using V350s. Three PLCs running the same software, having external hardware "outputs voting" and "minority voting" monitoring. The three PLCs are to be connected through RS485 (Modbus RTU) with a future SCADA. We have already implement, beyond the scenarios functions: - Alarm DBs (Actives, History), - Alarm Logging, - SD event logging Only the Com functions are incomplete. For our application : only an area of 100 coils (MBs), and another area of 100 registers (MIs) can be open (write enabled) to Modbus Write operations.

Dear Emil, the SCADA programmer can be any person with unknown skills. If he accidentally (or during his evaluation / debugging) writes into my PLC, the PLC application may run with no control. The result will be a disaster for the customer system. So, I would ask for an enhanced version of Modbus functions (it seems to me that this is provided in the Profibus functions), or another way to work around that issue, inside the PLC.

Dear Walkerok, thanks for the reply. I have seen your post, and I also noticed that you got no answer. The issue with the Write command blocking could be further extended, as the application may need the Master (a SCADA) to Write some MI or MB as user inputs to the PLC. In this case if the Write addressing is not correct (not rare at all) it could cause the PLC running with out any control as temporary registers (indexes, pointers, vector bases etc.) may be affected. I hope the Unitronics team to have a solution to this issue. Comment: It seems to me that in the Profibus and Allen Bradley protocols they have implemented it. Best regards, Nikolas

Hi all, in my application, a V350 will be a slave in a Modbus RTU net (RS485). I will provide, in a support text, the address map of the registers the Master (SCADA) should read to get the info required. But, in any case the Master (SCADA) should not be able to Write in the Slave PLC memory. As I have seen from the examples, activating the Modbus in the slave PLC enables the Master to Read and Write to any register in the PLC. Is there any way to block the Write command ? (The SCADA development is a future project, which may not be granded to me) Thanks