Patent ID: 7797461

Claim:
A programmable controller having a serial port for serial communication, comprising: a switching unit that switches the serial port in any one of a first state, a second state, and a third state, the first state being a state in which a general-purpose communication protocol which establishes the serial communication in accordance with a specification of a partner equipment can be processed, the second state being a state in which a computer link-only protocol which establishes the serial communication based on a fixed specification can be processed, and the third state being an idle state, wherein the switching unit switches the serial port to the first state by a first command that initializes the serial port in a program for the general-purpose communication protocol when the serial port is in the idling state, to the second state when the serial port receives a second command comprising a prefix value from external equipment, and the prefix value causing the switching unit to automatically trigger the serial communication using the computer link-only protocol based on the fixed specification, wherein no response to the second command is sent from the serial port of the programmable controller to the external equipment prior to automatically triggering the serial communication using the computer link-only protocol, and the serial communication with the external equipment is established based on only the received second command from the external equipment, to the idling state, upon the serial port being in the first state, by a third command that closes the serial port in the program for the general-purpose communication protocol, and to the idling state, upon the serial port being in the second state, after the serial communication with the external equipment using the computer link-only protocol is completed.