Exar (Nasdaq: EXAR) has introduced a groundbreaking addition to its single-chip RS-232/RS-485/RS-422 multi-protocol serial transceiver family with the launch of the SP338. This innovative device not only enhances Exar’s existing portfolio but also reinforces its leadership in the single-chip, multi-protocol transceiver market. Designed for industrial and embedded PC applications that demand a versatile serial interface, the SP338 offers exceptional flexibility and performance.
In RS-232 mode, the SP338 provides three drivers and five receivers, supporting the eight signal channels required by DB9 connectors (3TX/5RX). For RS-485 and RS-422 applications, it supports half-duplex, full-duplex, and hybrid configurations, with up to two drivers and four receivers (2TX/4RX). This versatility makes it an ideal solution for systems requiring seamless protocol switching.
Jack Roan, Technology Marketing Manager for Exar’s Interface Product Line, highlighted the significance of the SP338 and its counterpart, the SP339: “These two devices address one of the most challenging design issues—enabling and disabling termination resistors when switching between multiple serial protocols on a shared connector.†By integrating these features, the SP338 allows customers to reduce the number of external connectors, minimize component count, and ultimately lower both cost and product size.
The SP338 includes built-in termination resistors and control switches, enabling the system processor to manage termination resistors via a single pin. Additionally, the RS-485/422 mode incorporates open-circuit, short-circuit, and Exar-enhanced receiver fail-safe features, which eliminate the need for external resistor biasing networks and switching components when the bus is idle.
When using a shared connector between RS-232 and RS-485/422 protocols, the RS-485 termination and bias resistor must be disconnected for proper RS-232 communication. Due to the wide common-mode voltage range (-7V to +12V) in RS-485 specifications, expensive relays are typically required to switch these components. Most designers opt for separate connectors per protocol or manually switch resistors, resulting in increased size and cost. The SP338 eliminates this complexity.
Beyond its integrated termination resistors, the SP338 offers eight configurable modes, including diagnostic loopback, RS-232 (3TX/5RX), half-duplex RS-485, full-duplex RS-485/422, and hybrid duplex (2TX/4RX). It supports a maximum transmission rate of 20 Mbps for RS-485/422 and 1 Mbps for RS-232, with seamless mode switching via a single control pin. The device also features a slew rate of 256 kbps.
The internal charge pump generates the necessary bipolar voltage levels for RS-232 from a single 3.3V or 5V supply, using just four external capacitors. This eliminates the need for inductors or magnetic components, further simplifying the design.
All bus pins are protected against electrostatic discharge (ESD) with ratings up to ±15kV (Human Body Mode) and ±8kV IEC 61000-4-2 contact discharge, ensuring reliable operation in harsh environments. With its advanced features and flexible configuration, the SP338 is a powerful solution for modern serial communication applications.
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