Patent ID: 6880015

Claim:
A Modbus slave device operable in an agile mode, the slave device being capable of receiving, interpreting, and responding to first-type and second-type message frames, the slave device comprising: means for detecting a master query message frame generated by a master device; means, responsive to a first incoming character of the master query message frame, for setting a message-type control bit to a first value if the first incoming character is a prompt character for the first-type message frame, and for setting the message-type control bit to a second value if the first incoming character is not the prompt character for the first-type message frame; means for interpreting the master query message frame as the first-type message frame if the message-type control bit has the first value and as the second-type message frame if the message-type control bit has the second value; means for performing a command associated with the master query message frame if the slave device is addressed in the master query message frame; and means for generating a slave message frame responding to the master query message frame if the slave device is addressed in the master query message frame and the command requires a response, the slave message frame being of the first-type message frame if the message-type control bit has the first value, the slave message frame being of the second-type message frame if the message-type control bit has the second value.