Electronic Design

Single-/Dual-Channel UARTs Sport RS-485 Transceivers, Support 8 Mbits/s

The XR19L402/400 series are the first single- and dual-channel universal asynchronous receiver transmitter (UART) devices with integrated RS-485 transceivers to support data rates of up to 8 Mbits/s, according to their maker, Exar Corp. The UARTs offer different packaging and modem interface options. They operate from a single 3- to 5.5-V supply. The configuration register is 16550-UART compatible for control, status, and data transfer. Features include 64-byte transmit and receive FIFOs, automatic RTS/CTS hardware flow control, automatic Xon/Xoff and special character software flow control, transmit and receive FIFO trigger levels, and a programmable fractional baud-rate generator with a prescaler of divide by 1 or 4.

Both devices can operate in four different modes: active, partial sleep, full sleep, and power-save. Each mode can be invoked via hardware or software. Upon power-up, the device is in the active mode where the UART and RS-485 transceiver function normally. In the partial sleep mode, the internal crystal oscillator of the UART, or the charge pump of the RS-485 transceiver, is turned off. In full sleep mode, both the crystal oscillator and the charge pump are turned off. While the UART is in the sleep mode, the power-save mode isolates the core logic from the control signals (chip select, read/write strobes, address, and data bus lines) to minimize the power consumption. The RS-485 receivers remain active in each of these four modes.

The XR19L402 comes in a 48-pin QFN and is priced in the mid-$4.00 range in 1000-piece quantities. The XR19L400 comes in a 40-pin QFN, with a price in the mid-$2.00 range in 1000-piece quantities. To learn more, go to www.exar.com.

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