Abstract: A universal crystal-oscillator input/output (I/O) circuit is provided for use with an ASIC (Application Specific Integrated Circuit) device, and which can help enhance the electrostatic discharge (ESD) protection on the ASIC device in Charge Device Mode (CDM). This universal crystal-oscillator I/O circuit can help reduce the total number of I/O components in the ASIC library used to construct the IC device, allowing the design and management of ASIC library to be more simplified and convenient, making ASIC more cost-effective to implement. Moreover, this universal crystal-oscillator I/O circuit can help improve the performance of the oscillator circuit, allowing ASIC designers to have more convenience and flexibility in ASIC design. It can be fast in starting oscillation and low in power consumption.