A low pin count (LPC) bus serial interrupt system including a host and an external device sending interrupt signals to each other and exchanging signals with each other, the low pin count (LPC) bus serial interrupt system comprising: an interrupt direction signal generator configured to determine a current interrupt direction signal (SerIRQ_dir) according to whether the host currently sends a first interrupt signal to an external device ; and a level-shifter configured to receive the interrupt direction signal (SerIRQ_dir) in a static mode and to convert a voltage level of one of the signals exchanged between the host and the external device according to the current interrupt direction signal (SerIRQ_dir), wherein the first interrupt signal includes an end frame, wherein determining the current interrupt direction signal (SerIRQ_dir) by the interrupt direction signal generator according to whether the host currently sends the first interrupt signal to the external device includes: when the host currently sends the end frame to the external device , determining that the current interrupt direction is from the host to the external device , and generating a first signal indicating a direction from the host to the external device ; and when the host currently does not send the end frame to the external device , determining that the current interrupt direction is from the external device to the host , and generating a second signal indicating a direction from the external device to the host . an interrupt direction signal generator configured to determine a current interrupt direction signal (SerIRQ_dir) according to whether the host currently sends a first interrupt signal to an external device ; and a level-shifter configured to receive the interrupt direction signal (SerIRQ_dir) in a static mode and to convert a voltage level of one of the signals exchanged between the host and the external device according to the current interrupt direction signal (SerIRQ_dir), wherein the first interrupt signal includes an end frame, wherein determining the current interrupt direction signal (SerIRQ_dir) by the interrupt direction signal generator according to whether the host currently sends the first interrupt signal to the external device includes: when the host currently sends the end frame to the external device , determining that the current interrupt direction is from the host to the external device , and generating a first signal indicating a direction from the host to the external device ; and when the host currently does not send the end frame to the external device , determining that the current interrupt direction is from the external device to the host , and generating a second signal indicating a direction from the external device to the host . when the host currently sends the end frame to the external device , determining that the current interrupt direction is from the host to the external device , and generating a first signal indicating a direction from the host to the external device ; and when the host currently does not send the end frame to the external device , determining that the current interrupt direction is from the external device to the host , and generating a second signal indicating a direction from the external device to the host . <EOS>