Sequence control apparatus

In a programmable sequence control apparatus comprising:

• a first memory for storing a plurality of sequence program instructions, a relay ladder operation unit for executing logic operation simulating an real relay ladder circuit having n rows and m columns (n and m are positive integers), an input/output control unit which is connected with input and output elements for introducing input data representing logical states of the input elements and delivering output data representing logical states of the output elements, said input data being used in said ladder operation unit as a contact data, and a control unit responsive to said each program instruction for delivering control signals to said relay ladder operation unit, the improvement wherein said input/output control unit has a second memory for storing said input and outut data, each of the addresses in said second memory being related to a position in said relay ladder circuit defined by a pair of column's and row's members;
• each of said program instruction in the first memory includes information concerning said position, which includes addresses corresponding to said input or output elements, a branch data representing whether one row corresponding to an address in a column is connected directly with one directly below in the subsequent column or not, and a line data representing whether the row in said column is the last (or bottom) one or not;
• said relay ladder operation unit has a plurality of logic circuits equal to the number of columns in the relay ladder circuit, each of said logic circuits comprising:
• a first shift register for storing said contact data, a second shift register for storing said branch data and a gate circuit which receives said contact and branch data being stored in said shift registers for producing a plurality of signals, each of signals representing logical state of each row in one column, and
• a memory for storing output data which is formed when all of contact and branch data in one sequence cycle are registered in said first and second shift registers, said control unit firstly decodes said program instructions consecutively and supplies decoded branch data and the corresponding contact data fetched out of said second memory to said logic circuits, and
• simulation of said relay ladder circuit in one sequence cycle terminates when said control unit decodes all program instructions, and all of the contact and branch data corresponding to said each position in the ladder circuit are registered in said shift registers.