One of my clients approached me and inquired about bridging the data in an existing Siemens S7-224 to his MetasysN2 system. This was certainly a first for me; however, I did a little research of the Metasys system and found that Modbus was among it's many configureable protocols.... So, now it seems simple: Just configure the communication port of the Siemens S7-224 for Modbus and my problems are solved...or so I thought. First of all, if you configure the single communication port on a Siemens S7-224 for Modbus, you open up a whole can of worms. First of all, you must enable the S7-224 to 'speak' Modbus. For this, you have to purchase the Modbus Library expansion. You load this addon to your Siemens MicroWin and you're done. You can now configure your S7-200 PLC via the register editor to dump contents of identifed registers into 40000 series registers.

Now that I had the S7-224 communicating in Modbus, I thought I was half way home. To enable the S7-200 to communicate in Modbus, you must configure the communication port to work via RS232. If you dedicate the comm. port for Modbus communications, then you have no programming interface port. The asnswer to this problem was also simple: Replace the S7-224 with a S7-226, which comes standard with two (2) serial communications ports. Once I had my S7-226, I configured port 1 to be my programming (user) interface, and I configured port 2 to by my dedicated Modbus interface to my MetasysN2 bridge. Now, the only issues left to resolve was to find a gateway which would bridge my S7-226 with the MetasysN2 system.

I did a Google search using "MetasysN2 Modbus" as my search terms and my search results directed me to Protocessor.com. I reviewed the site and found that the Protocessor Protonode would be a perfect candidate to bridge my S7-226 to the MetasysN2 system. Once I received the Protocessor Protonode, I downloaded the Fieldserver utilites on the Protocessor site and found them to be easy to install and very easy to use. I had my Protonode working quickly and the results were easy to verify using the data view within the Fieldserver utilities. I was able to view the real-time updates of the discrete I/O and register data with my Siemens S7-226. My customer was happy with the results and I gained some valuable experience with Siemens S7-200, MetasysN2, and the Protocessor Protonode.

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