Herein, we explore the potential of OECDs as building blocks for neuromorphic systems by employing organic mixed ionic-electronic conductors as an active layer. By modulating the ionic flow between the source and drain, it causes changes in the actual potential of active layer. Therefore, the conductivity of the active layer could be regulated under the forward bias below 0.8 V, leading to organic synaptic diode. We also demonstrated the learning-forgetting-relearning process, where the conductive state can be recovered with 5-time less stimulation. Finally, the integration of multiple neuromorphic devices into a digital circuit leads to the realization of programmable logic gates which could selectively become AND or OR logic depending on the training method. Our results successfully demonstrate the novel device operation mechanism and the digital circuitry realization in the field of organic neuromorphic device development.