Attached here are modified BasicDataLogger2 and DataSubscriber2 components.
There is a new PLCAddressWriteOnBitTrue property which allows you to specify the address for the bit.
When this bit goes True then values for all addresses in the PLCAddressValueItems will be logged (a choice of DataChanged or DataReturned values is also included).
You would have to replace both stock components with the attached ones.
The attached log file was created at Runtime, with following Modbus settings:
PLCAddressWriteOnBitTrue = 00001
PLCAddressValueItems = 40001, 40002
If you check the times, the bit 00001 was ON two times for a certain length of seconds while values for both 40001 & 40002 addresses were logged.
Also attached are modified BasicDataLogger and DataSubscriber components, with identical features but for single address.