The 73K222AL is a highly integrated single-chip modem IC which provides the functions needed to construct a CCITT V.22, V.21 and Bell 212A compatible modem, capable of 1200 bit/s full-duplex operation over dial-up lines. The 73K222AL is an enhancement of the 73K212L/AL single-chip modem which adds V.22 and V.21 modes to the Bell 212A and 103 operation of the 73K212AL. In Bell 212A mode, the 73K222AL provides the normal Bell 212A and 103 functions and employs a 2225 Hz answer tone. The 73K222AL in V.22 mode produces either 550 or 1800 Hz guard tone, recognizes and generates a 2100 Hz answer tone, and allows 600 bit/s V.22 or 0 -300 bit/s