These days reflect our so-called communication era, and the data processing industry has been growing at a tremendous rate, particularly in the area using the existing telephone networks. The modems are playing an important role as an interface to computer systems which communicate by a public or dedicated data transmission networks. Taking early notice of the significance of data communications, OKI has been engaged since many decades in the development and manufacturing of data communication-related equipments. This application note introduces and explains OKI’s latest development in this field, the CMOS Single-chip modem series, MSM6926, MSM6927,MSM6946, and MSM6947. Before entering details of this new series, let us first see what a modem is all about. 1) What is a modem? 2) Modem communication systems 3) Modem types and modulation/demodulation methods