What is your engineering workstation stops communicating to the ABB DCS controllers. Based on my past experience, 99.9% of time the it is due to hung IET800 card. I don’t really know why it hangs but I sure do know how to recover from the hung IET card.
The IET card that I am using is the Symphony Plus IET800. As shown below.
Basically, you will have to reset the card by poking the reset switch using a paper clip. Reset switch location as show above.
This is what your IET800 card looks like when it is hung. All the LED are static; except for the Ethernet port.
Video below shows what the LED looks like as you reset the IET800 card.