Abstract: An interface for synchronizing the output of standard asynchronous terminals with a PABX allows all terminals to operate asynchronously with respect to each other. The output from the I/O terminal, which comprises a binary data stream in an asynchronous code, is sampled at a rate of at least three times greater than the output bit rate of the terminal. A clock signal to effect the sampling is generated within the PABX. The sampled data appears to the PABX as a bit stream synchronized with the PABX clock, allowing direct application of the sampled data to the PABX. The receiving terminal, upon reception of a start bit, waits one-half time (of its own clock) and samples the received data to reconstruct the received bits into corresponding alphanumeric characters. The frequency of the clocks internal to each terminal may vary within one percent of each other before requiring each terminal to be synchronized with each other.