Hi u5726082, Welcome to EasyEDA. EasyEDA uses the free and open source software ngspice for simulation. Part of ngspice is XSPICE. XSPICE can be used as the basis of simulation for digital devices. However, to simplify mixed mode simulation in EasyEDA, we have developed a set of basic digital devices or primitives built using XSPICE that can be used to put together more complex functions. There are also several devices available that are representative of packaged logic devices such as 74HC00 quad NAND gates, 74HC74 dual D type flip flops and 74HC4060 oscillator/counters. These can be found in the **EasyEDA Libs** under **Gates**. More information and examples of some of the devices can be found here: >https://easyeda.com/project_view_Easy-logic-device-simulation-in-V2.3.x- onwards_RaKIG2oJ5.htm In particular, please see: >https://easyeda.com/file_view_About-the-EasyEDA-logic-devices_VoYkiECXV.htm