Safely Converting SIngle Ended encoder signals to Differential....?????

Hi All,

I am converting sigle ended encoder signals to Differential signals using the AM2631 IC but the problem is that if one wire is broken or even whole cable is broken near encoder (before Line Driver circuit)then the output of the AM2631 remains standard A,/A,B,/B,Z and /Z and the CNC control does not give fault of Encoder wire break in the result the problem axis runaway in accident state.
Is there any way to improve the Driver circuit?? I think the solutionlies in something to do with enable pins of AM2631, but I am not sure how to use these..

Please advise....

Regards