An interface circuit provides communication between a memory card and a host device which use a half duplex communication protocol. The interface circuit switches communication direction between the host device and memory card by analyzing interface protocol. The interface circuit includes a sending packet analyzing module which receives a first signal packet from the host device and obtains working status of the host device and memory card by analyzing the first signal packet, a bus direction control module coupled to the sending packet analyzing module which generates a first control signal according to a first parameter in the first signal packet which includes conducting direction information indicating the host device between the memory card, and a direction switching module coupled to the bus direction control module which controls the conducting direction of the pathway between the host device and memory card according to the first control signal.