As master unit and the slave who

摘要

PROBLEM TO BE SOLVED: To provide a field bus system communication speed control method capable of making communication possible up to a disconnection part even when communication is disconnected.;SOLUTION: A master unit 12 constituting a PLC 10 and a slave 20 are connected to a bus type field bus 30 and a terminal resistor 31 is connected to the terminal of the field bus 30 to constitute the field bus system. When the system functions normally, the master unit 12 and the slave 20 communicate with each other at high communication speed where the terminal resistor is necessary, and when the field bus is disconnected, the master unit 12 switches the communication speed to a lower communication speed at which communication can be performed even when the terminal resistor is absent to continue the communication.;COPYRIGHT: (C)2004,JPO&NCIPI