The 73K321L is a highly integrated single-chip modem IC which provides the functions needed to construct a CCITT V.23 and V.21 compatible modem, capable of 0-300 bit/s full-duplex or 0-1200 bit/s half-duplex operation over dial-up telephone lines. The 73K321L provides 1200 bit/s operation in V.23 mode and 300 bit/s in V.21 mode. The 73K321L also can both detect and generate the 2100 Hz answer tone needed for call initiation. The 73K321L integrates analog, digital, and switchedcapacitor array functions on a single substrate, offering excellent performance and a high level of functional integration in a single 28-pin DIP or PLCC package. The 73K321L operates from a single +5V supply with very low power consumption.