Programmable controller with direct to plant addressing

A programmable controller for controlling the operations of a plant on the basis of a stored program, comprising:

• memory means for storing therein a program, said program containing an instruction taking a register-modified addressing mode as an addressing mode of an operand and an instruction taking a direct addressing mode as the addressing mode of an operand, each of said instructions being read out from said memory means in response to receipt of a corresponding memory address;
• a processing unit provided with operating means for supplying an address to said memory means to read out an instruction from said memory means and for performing an arithmetic operation in accordance with said read-out instruction to control a process, including an instruction register for storing an instruction read out from said memory means, means for determining by the contents of the instruction stored in said instruction register whether said instruction is an instruction taking the register-modified addressing mode or an instruction taking the direct addressing mode, a plurality of index registers, an arithmetic circuit, switching means for delivering an address as address information for controlling a plant in such a manner that, when the instruction stored in said instruction register is of the register-modified addressing mode, the contents of an index register specified by an index part of said instruction are added to an address indicated by the address part of said instruction by said arithmetic circuit and the result of addition is delivered as address information for controlling a plant, and when said instruction is of the direct addressing mode, an address indicated by an address part of said instruction is directly delivered as address information to said plant, and control circuit means for controlling said switching means in accordance with said determining means and for controlling said arithmetic circuit to operate on state information received from the plant in response to an address supplied to the plant via said switching means to produce control information to perform control operations in accordance with a command from an operation code part of the instruction read out from said memory means and stored in said instruction register;
• and
• a process input/output unit disposed between said processing unit and said plant and responsive to said plant control address information from said processing unit for sending control information which is outputted from said processing unit to a plant specified by said address information and for sending state information which is inputted from said plant to said processing unit.