This paper describes the design details and the characterization of an all digital closed-loop (ADCL) interferometric fiber optic gyroscope (IFOG) Prototype with sine wave biasing modulation and SLED emiting at 1288.9 nm, constructed in TUBITAK UME. Electronic feedback section of ADCL-IFOG is composed of 16 bit AD7714YN ADC, 14 bit-LTC1667CG DAC, fully controlled and synchronized by 89C51 microcontroller. The averaged sensitivity of the ADCL-IFOG prototype in unit of error voltage applied to the phase modulator was calculated as 132.65 mu V/(A degrees/h) which equals to a scale factor of 7.53888 (A degrees/h)/mV with a standard deviation of 0.85% for a range of 1-15270 (A degrees/h) rotation rate, corresponding to a range of Sagnac phase shifts varying from 0.00115 to 17.57448 (A degrees). The maximum peak to peak noise and the bias stability of the prototype were determined as 4.97 and 1.48 (A degrees/h) at 23.0A degrees C, respectively. The variation of the noise and bias stability on a temperature range of 23.0-42.0A degrees C was observed.