Abstract: A method and apparatus for transmission of data among computers or peripherals along a loop transmission line includes a master system which provides signals along the transmission line for establishing a series of data frames of equivalent length. Each data frame is assigned a frame number, and is allotted a preselected amount of available space for placement of data. Subsequent computers or peripherals are preprogramed with a series of frame numbers which identify those data frames into which they may write data, or from which data is to be read. The allotment of preselected frame numbers for placement and reception of data by the respective devices provides for equivalent sharing of the available data transmission capability of the loop transmission system.

Abstract: A programmable controller for controlling a plant on the basis of a stored program includes a processing unit for reading out an instruction from a program memory to process the instruction. In the processing unit, it is determined whether the instruction read out from the memory is an instruction taking a register-modified addressing mode or an instruction taking a direct addressing mode. When the read-out instruction is an instruction taking the direct addressing mode, a plant is directly addressed by the address part of the instruction. Then, an arithmetic operation is performed using the state information which is read out from the plant thus addressed, or plant control information is sent from the processing unit to the plant thus addressed.