Abstract: In a sequence program constructed by forming a ladder diagram on a display screen, an element corresponding to a minimum unit of the ladder diagram is arranged by a symbol element and a character element. Inputting and amending operations of the ladder diagram are performed by a first cursor for designating each element and a second cursor for designating the character element of the element designated by this first cursor.

Abstract: An input/output device has a processor which processes data strings received by the device. When a data string is received, it is passed to a serial interface and a timing means. The serial interface generates a signal which interrupts the existing processing by the processor and causes the process to start processing of the newly received data string. At the same time the timing means measures the length of the data string and compares it with a predetermined length set by user-controllable data setting means. If the data string length reaches the predetermined length, the processor is triggered to stop processing the new data string and to recommence the processing it was performing prior to interruption. The unprocessed part of the new data string is stored in a memory.In this way, urgent data strings, which are generally short, are processed rapidly and longer data strings are processed after the urgent data strings.

Abstract: A built-in insulating element for electrically insulating a process portion from a control object and for transmitting a process result to the control object is provided in the output portion for transmitting the process result of a sequence controller to the control object. Further, a noise preventive element is provided in the output portion for preventing a noise voltage from coming in from the control object side and damaging the insulating element.

Abstract: A programmable sequence controller has indicator lamps for displaying the status of the respective input and output signals. The indicator lamps are respectively coupled with signal input and output terminals through a connector, and are included as in a panel which cover the front surface of the signal input and output terminals.

Abstract: Data processing between selected I/O terminals is switched between processing by direct access to the I/O terminals and processing by indirect access through an image memory having a one-to-one correspondence to the I/O terminals.