Abstract: A synchronous digital transmitter connects a data terminal equipment to a multiservice digital PABX which accesses the public switched telephone network at 64 kbit/s. It includes a system for generating a frame clock defining a 64 kbit/s data transmission channel used for the transmission of data to and from the PABX. A further system generates a bit clock at the same frequency as the data from the terminal equipment for transfers to and from the terminal equipment. A further system periodically synchronizes the bit clock to the frame clock. The transmitter is applicable to the synchronous transmission of data at data rates up to 64 kbit/s.