Hi Friends, Hai .. friends , I have problem with PLC C200H At mymachine I put PLC C200H and I instal NT20M for display and some Remote I/O. Master Remote I/O I give C200H-RM201. This machine is about 5 years old. Since last month , it has some trouble , Normaly in for numeric display will 12345 displayed , but some times only ***** displayed . So At PLC , error lamp is flash and at Master remote I/O error lamp is flash . PLC still RUN I think NT20M is broken , so I change NT20M with new . But the the trouble is same . I check PLC with programmer console . It says for check transmission betwen PLC and Master remote I/O and remote moduls . So . how to check transmission ? Anybody , please help me to take this trouble. Thank,s yono