ADM1485 bus open circuit failure detection with termination

Hi All,


My customer is using ADM1485 for his equipment.

One pair of ADM1485 are controlled by one CPU, it means both of DE and /RE are controlled by one CPU, and the data is sent and received between two ADM1485s.

It also needs the bus open failure detection under termination (120ohms) connected.

Some of his board shows unstable bus open failure detection with 120 ohms termination.

His question is that is it okay to set both side of DE terminal to high temporarily, such as 1msec long?

He said that both side of ADM1485 is set to drive mode simultaneously. This is illegal condition, he understood. However during this condition, both side of DI is the same logic level. So he is considering that this will not cause erroneous operation such as high current flow on A or B line in normal condition (not open bus condition).

He has been trying to solve the bus open failure detection correctly with 120ohms termination, and find that setting the both side of DE to “high” forces RO to “high” with termination.

He would like to hear your advice on this approach.


Best Regards,