The M-991 is a call progress tone generator integrated circuit for use in telephone systems. The circuit uses low-power CMOS techniques to generate tones which are digitally controlled and highly linear. The M-991 is designed to permit operation with almost any system. The use of integrated circuit techniques allows the M991 to incorporate the control, tone generating, and power output buffer into a single 14-pin DIP or a 16-pin SOIC. A 3.58-MHz (color burst) crystal-controlled time base guarantees accuracy and repeatability.