A single-chip 300 baud FSK modem

A 300-baud single-chip FSK modem implementing an RS-232 interface handshaking protocol is described. The device is a full duplex asynchronous modem that meets both Bell 103 and CCITT V.21 specifications. It incorporates the protocol required for automatic answer/originate, loss of carrier termination, and a 14-s abort timer. The device also implements analog and digital loopback capabilities for local and remote testing, respectively. The chip is implemented using a double-poly CMOS technology and uses a standard 3.58-MHz colorburst TV crystal. Inclusion of the handshaking protocol facilitates interfacing the modem to a standard RS-232 interface in stand-alone applications, or a UART in other applications, where the modem is integrated into the data terminal equipment.