| 摘要 |
PURPOSE:To attain the effective utilization of a transmission line used in common by transmitting a transmission request flag to the prescribed position of a frame when a terminal device transmits a data to the other device and allowing a CPU to detect the flag to designate the terminal device at the next frame number. CONSTITUTION:The CPU4 and terminal devices 1, 2, 3 are connected by a transmission line 5 of the multi-drop system, and the devices 1, 2, 3 and 4 are provided respectively with transmission circuts 11, 21, 31 and 41 and receiving circuits 12, 22, 32 and 42. When the terminal device 3 transmits a data to the other device, a transmission request flag is transmitted to a Tm+n+1 of the FLAG of the frame at that time. When the CPU4 detects this transmission request flag, ''3'' is transmitted as the No. of the next frame, and when the device 3 confirms it, a data is transmitted to a DATA part of the frame. Further, the CPU4 brings the No. to ''O'' when no transmission request flag exists in the FLAG, and transmits a data to be transmitted from the devices 1, 2 and 3 from the CPU4 to the DATA part. |
