The Modbus Utility location: http://ftp.icpdas.com/pub/cd/8000cd/napdos/modbus/modbus_utility/ or The eSearch Utility (v1.1.6 or later) supports "Modbus RTU Master" and "Modbus TCP Master" items in the "Tools" menu that two programs are useful for testing. The eSearch Utility location: http://ftp.icpdas.com/pub/cd/tinymodules/napdos/software/esearch/