Backup only ssd not ssd+hdd

[Husky1992]

Hi
I have a mbp with an ssd installed and a second hdd installed in the tray for data
Is there a way, with time machine, to backup onto an external hdd ONLY the system ssd disk? I can't find the option and if I try to start the backup it backups onto the external drive the ssd AND the hdd

 

[Alrescha]

System Preferences/Time Machine/Options:

Under "Exclude these items from backups:" hit the plus sign "+". Navigate to the drive you want to ignore and hit the Exclude button.

A.