| 摘要 |
PURPOSE:To prevent the collision of data on a transmission line and reduce the loss of time by controlling plural stations connected to the common transmission line so that data is transmitted or inhibited in accordance with a detection signal which detects the presence or the absence of data on the transmission line. CONSTITUTION:A master station MST10 and slave stations SSTs 201-20n are connected to a common transmission line L in the multidrop system. A detecting circuit 15 of the MST10 outputs a detection signal 17 of logical ''0'' to a microprocessor muPC12 on a basis of the reception output from a receiver 14 if data does not exist on the transmission line L. Then, the muPC12 inverts an output permitting/inhibiting signal 13 from logical ''0'' to logical ''1'', and a driver 11 is permitted to output data, and required data from the muPC12 is transmitted to the transmission line L through an interface circuit 16. If the circuit 15 outputs the signal 17 of logical ''1'', the muPC12 judges that data exists on the transmission line L, and the signal 13 is set to logical ''0'' to inhibit data transmission from the driver 11. In each SST20i, similar operations are performed. |
