EUCLID is an ESA mission intended to investigate dark energy by measuring the redshift of distant galaxies with an unprecedent accuracy. This will help physicists and astronomers to better understand the origin of our universe. One of the main characteristics of EUCLID spacecraft is its attitude control capabilities, as they need to be very precise to perform the scientific measurements. The units that give EUCLID this characteristic are part of the AOCS (Attitude and Orbital Control Systems), being one of them the Fine Guidance Sensor (FGS). FGS EU is intended to communicate with the spacecraft onboard computer (CDMU), execute procedures of image processing, manage the internal modes by use of the Application Software (ASW) and Startup Software (SUSW), manage the power supplies for PEMs (Proximity Electronics Modules) and compute attitude of the spacecraft given the data coming from detectors.