The DS276 Line-Powered RS-232 Transceiver Chip is a CMOS device that provides a low-cost, very low-power interface to RS-232 serial ports. The receiver input translates RS-232 signal levels to common CMOS/TTL levels. The transmitter can be used with independently supplied positive and negative supplies, but in most cases will be used with the positive supply, sharing the logic supply and the negative supply stolen from the receive RS-232 signal when that signal is in a negative state (marking). By using an external reservoir capacitor and Schottky diode (see Figure 4) this negative supply can be maintained even during full-duplex operation. Since most serial communication ports remain in a negative state statically, using the receive signal for negative power greatly reduces the DS276's static power consumption. This feature is especially important for battery-powered systems such as laptop computers, remote sensors, and portable medical instruments. During an actual communication session, the DS276's transmitter will use system power (3-12 volts) for positive transitions while still employing the receive signal for negative transitions.