What are you meaning by “work together”?
Are you meaning linked together so that the units share some form of data between them or are you meaning that both can be run on the same boat at the same time without interfering with one another?
With the 797 unit you are limited to the InterLink accessory for linking it to another unit.
With two sonar units on the same boat there is always the possibility of getting sonar-to-sonar interference as most of our units use the same 200kHz frequency for the 2D sonar. If you do get this; try turning on and up the Noise Filter menu on the unit that is showing the interference. If that does not help enough than try setting the Lower Range menu to a manual setting that is different than the other unit.