Actually, the Siemens controller you are using is equivalent to an Automationdirect.com D3-330 or D3-340. The D3-350 is compatible with your hardware, but uses a different programming. The software doesn't make a difference, but don't try to replace a Simatic 325 with a D3-350. I would however, suggest you get you hadware for this PLC from Automationdirect.com. They are continuously updating their products and are much cheaper than Siemens. Note: The GE Series 1, the Texas Instruments TI305, and the Koyo SR21 are also 100% compatible with the Automationdirect and the Siemens.