PROBLEM TO BE SOLVED: To efficiently perform cyclic data transfer, while considering the transmission data amount of respective programmable controllers (PC).;SOLUTION: Based on the responsiveness of a system or data amount of respective PC, edition information such as the total number of time slots, allocated time slot number and time slot time is set from an engineering tool to a transmission timing determining device 27 of each PC 1. When reception is interrupted, an MPU 24 compares the transmission source time slot number of a received data frame with its own time slot number and when it is its turn, transmission processing is performed by activating the time slot timer of a time measuring device 25. At that time, the number of continuous time slot numbers allocated to the MPU itself is managed and for transmission time after the second serial number, each time of transmission processing of the preceding number, the time slot timer is activated and determined synchronously with time slot time. The number of time slots to be allocated to each PC can be set corresponding to the transmission data amount, and the transmission efficiency of a serial bus is improved.;COPYRIGHT: (C)2000,JPO
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