MAX3140

19-1453; Rev 0; 6/99 SPI/MICROWIRE-Compatible UART with Integrated True Fail-Safe RS-485/RS-422 Transceivers General Description The MAX3140 is a complete universal asynchronous receiver-transmitter (UART) and a true fail-safe RS485/RS-422 transceiver combined in a single 28-pin QSOP package for space-, cost-, and power-constrained applications. The MAX3140 saves additional board space as well as microcontroller (µC) I/O pins by featuring an SPI™/QSPI™/MICROWIRE™-compatible serial interface. It is pin-programmable for configuration in all RS-485/RS-422 networks. The MAX3140 includes a single RS-485/RS-422 driver and receiver featuring true fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open or shorted. This feature provides immunity to faults without requiring complex termination. The MAX3140 provides software-selectable control of half- or full-duplex operation, data rate, slew rate, and transmitter and receiver phase. The RS-485 driver slew rate is programmable to minimize EMI and results in maximum data rates of 115kbps, 500kbps, and 10Mbps. Independent transmitter/receiver phase control enables software correction of twisted-pair polarity reversal. A 1/8-unit-load receiver input impedance allows up to 256 transceivers on the bus. The MAX3140’s UART includes an oscillator circuit derived from an external crystal, and a baud-rate generator with software-programmable divider ratios for all common baud rates from 300 baud to 2...