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-~SSI73K222USingle-Chip Modemwith UARTPIN DESCRIPTION (continued)UART INTERFACE (continued)TXD 7 9ANALOG I LINE INTERFACENAME DIP PLCCTXA1 3 4TXA2 4 5RXA 16 18SPKR 17 19OH 18 200TYPE00I00Function is determined by STNDLN pin and bit 7, ToneControl Register:-~.--- ---"'._-STNDLN D70 0 TXD is a serial output of UART.1 0 TXD is forced to a mark.X 1 TXD is a serial output of UART.DESCRIPTION(differential) Transmitted Analog. These pins provide theanalog output signals to be transmitted to the phone line.The drivers will differentially drive the impedance of the linetransformer and the line matching resistor. An externalhybrid can also be built using TXA 1 as a single endedtransmit signal.Received Analog. This pin inputs analog information that isbeing received by the two-to-four wire hybrid. This inputcan also be taken directly from an external hybrid.Speaker Output. This pin outputs the received signal througha programmable attenuator stage, which can be used forvolume control and disabling the speaker.--Off-hook relay driver. This signal is an open drain outputcapable of sinking 20mA and is used for controlling a relay.The output is the complement of the OH register bit in CR3.3-82