Modbus® is an industrial Transmission Control Protocol (TCP), a vendor-neutral communication protocol intended for the supervision and control of automation equipment and used for remote monitoring and control applications. This portable embedded stack describes a Modbus TCP server and client implementation and how it can be extended in a Modbus application. The demo application software was developed using Utthunga’s TCP/IP stack. Although the software was developed and ported on Renesas' RA6M4 MCU, it is easily ported to other Renesas RA microcontrollers that support TCP/IP functionality.