The point of a reusable function block is to wrap up complex or repetitive code and make a simple and easy to use interface in order to use that code. The way you interface to a function block is critical for program efficiency, readability, and development time.

Interfacing to an instance of a function block It is worth mentioning that both platforms adhere to the IEC-61131-3 standard, which means that function blocks are available and can be written in any of the standard's languages. Why use function blocks, you ask? You must read the DMC blog: ' IEC 61131-3 Function Blocks - Unleash the Power!' Since this feature was only added in 2007, it is often overlooked and doesn’t fit as seamlessly into the overall environment. In AB’s RSLogix 5000 version 16 and higher, reusable function blocks are called Add-On Instructions (AOI) and can be defined with interface parameters and local tags. Function blocks are a fundamental concept in the Siemens platform, which give them a significant advantage for large, modular applications.

Siemens uses the term Function Block (FB) for program routines that can have internal memory, as opposed to Function Calls (FC) that have only temporary internal memory.

Allen-Bradley (AB) - RSLogix 5000 for the Control Logix and Compact Logix PLCsĪs someone who uses both platforms regularly, I would like to compare one of the key differences between them - function blocks.

Siemens - Step 7 Simatic Manager for S7-300 and 400 level PLCs.

On the higher end of their PLC lines, the programming environments to use are: A cursory Google search will reveal that there is no lack of debate among automation professionals over which one is preferred. Rockwell (aka Allen-Bradley) seems to be more popular in the US market, but Siemens has a larger international customer base. Siemens and Rockwell Automation are two giants competing in industrial automation technology today.

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