FactoryLink SCADA--> PLC5 and SLC504 via DH+

[garypeme]

Hi I am imminently going to be performing a FacoryLink SCADA Driver trial. This trial will consist of communicating to one PLC5 and one SLC504 over DH+. Given my lack of experience with DH+ I was wondering if anybody had any tips/guidance. I believe I am required to place MSG instructions in the PLCs, but what do I define in the destination address given that I am communicating with a SCADA system, not another PLC? Also, can anybody tell me what the difference is between a Classic PLC5 and Extended PLC5. Your help would be greatly appreciated.

[Ken Moore]

You will need some type of DH+ interface card in the PC, and a driver for communication with the PLC's. The PC will read and write to and from the PLC's, not the other way around. The MSG instructions primary purpose is to pass data between PLC's. I believe it's enhanced, not extended. The enhanced PLC-5's have a larger instruction set, better communication options (including a serial port), and generally speaking, can handle much larger programs, and support more remote I/O.

[garypeme]

Hi Ken Thanks for your reply. Have procurred the KT PCI card for PC and the FactoryLink Drivers. Are you saying that I will not require any DH+ comms code (ie MSG instruction) in my PLC as the PC will handle all the reads and writes? So all I would need to do PLC end is address the PLC correctly and just have my user program required for the test (lots of block transfers)? Cheers Gary

[BobLfoot]

This is an area for a lot of confusion. Perhaps I can elaborate. 1. You can set up your SCADA so that all reads and writes are done from the PC and no MSG instructions are required. This is the simpliest method and is most commonly used by beginners. IT has the advantage of simplicity and ease. it has the disadvantage of needing to be always polling the PLC creating network traffic and it is asynchronus to the PLC process so that results can be unpredictable if not allowed for in programming style. 2. You can set your SCADA so that the PLC sends Messages to the PC. This requires the use of a driver that supports Unsolicited messges {RSLInx for ex}. This has the advantage of limiting network traffic to being event based. PLC sends message at event and PC sends response. It has the disadvantage of being more sophisticated than option 1 and therfore takes longer to setup and debug usually. For what you describe I'd try option 1 and only migrate to option 2 if the application grows in scale.