Abstract –  In this paper, technical detail to develop Modbus compliant device and get conformance certification for a product will be explored. The information provided in this paper is not available in a single document or web link and there are many corner cases to take care of while developing a Modbus compliant device, this is the motivation for me to publish a paper. The information provided in this paper will help manufacturers in developing their Modbus compliant products and getting the conformance certification from the authenticated labs. Based on the experience we have gained so far, I am sharing the technical guideline to be followed to develop a Modbus compliant device and penetrate the market as a certified device manufacturer. This paper contains advanced technical information, so the basic understating of the  Modbus protocol is mandatory.