The SN75LBC784 is a RS-423-B combination driver/receiver offering four independent drivers and four independent receivers in a single 28-pin package. The RS-423 standard is designed for serial data transmission similar to RS-232, but at much higher data rates over longer cables. The SN75LBC784 provides the capability to send more data over longer distances, with increased reliability. Backward compatibility can be maintained with existing RS-232 equipment by adding external resistors to meet the RS-232 input resistance specification of 3 kOhms to 7 kOhms. The V.34 modem specification calls for the use of RS-423 communication devices for external modems in order to achieve the data rates without violating the data communications standards. With its high data transfer rate, the '784 is well-suited for PC to V.34 modem applications.
With the slew rate control pin connected to 5 V externally, the driver can support transition times to 1.5 µs, and typical receiver transition times of 20 ns. With RS-423-B, the data rate is increased to 120 kbps and transmission distance to 1.2 km. This is done by reducing the maximum output signal swing, increasing the driver output current, and reducing the receiver input voltage thresholds. While some devices that were designed to meet RS-232 standards might operate at RS-423 speeds, the SN75LBC784 is designed for these speeds and guaranteed by standard to reliably send and receive data, regardless of the manufacturer of the RS-423 parts at the other end of the cable. The SN75LBC784 is available in the 28-pin wide body SOIC (DW) package.
Vol 11, Spring, 1995