This paper presents an asynchronous peer-to-peer simplex/duplex-compatible communication system. The channels are based on a 1-phase signaling scheme that has the simultaneous handshaking and delay insensitivity, which achieves not only high-speed but also robust communication to variations of wire delays. A transmission is controllable by adding a mode-detection channel that observes the mutual states in both ends. Since current sources are appropriately controlled depending on mutual states, the power dissipation can be greatly reduced when both ends are on standby. Moreover, both simplex and duplex communication can be realized by sharing a common circuit except a signal-level conversion circuit. The proposed interface is implemented and evaluated using 0.18-μm CMOS, and its performance and efficiency are discussed.