Devices enable 9Mb/s throughput across four UART channels

ESD protection integrated on the USB pins eliminates the need for additional protection components and reduces PCB real estate required. An internal oscillator removes the need for an external crystal, further reducing the required board area. Powered directly from the USB host’s 5V supply, the USB to serial bridge devices integrate an LDO which provides a regulated 3.3V power supply output. This removes the need for an external LDO and saves further board space. The XR21B142x family is suitable for rugged applications such as smart grid data collection, data aggregators and concentrators, security and access control systems, ATM and gaming terminals and USB to serial converters.

According to the manufacturer, the USB to serial bridge devices offer significantly higher data throughput compared to competing devices, particularly with multiple channels in simultaneous operation. The family features 512B transmit and receive FIFOs enabling a maximum data throughput of 9Mb/s across up to four UART channels. Supporting USB suspend, resume and remote wakeup operations, the XR21B142x family can generate any baud rate up to 12Mb/s with the internal clock and the fractional baud rate generator.

Using native OS CDC-ACM drivers, or a custom driver to activate advanced features, the XR21B1420, XR21B1422 and XR21B1424 devices provide one, two and four UART channels, respectively. The XR21B1421 provides a single channel UART and uses the native operating system Human Interface Device (HID) driver in Windows, Linux, and Mac OS X distributions. This eliminates the need to install custom drivers and, therefore, simplifies the integration process. Exar also offers WHQL/HCK-certified software drivers for Windows 2000, XP, Vista, 7, 8 and 8.1 as well as drivers for Windows CE, Linux and Mac OS X.

In order to simplify hardware and software in half-duplex RS-485 applications, the XR21B142x devices feature automatic half-duplex direction control and optional multi drop (9-bit) mode. Full modem control signals on each UART port can be configured as GPIO pins with direction, state, output driver type and input pull-up or pull-down resistors programmed through on chip OTP or via memory mapped registers.

The XR21B1424 is available now in a 64 LQFP. With sampling starting this month, the XR21B1420/1 devices are supplied in a 24- or 28-pin QFN package. The XR21B1422 is offered in a 40-pin QFN package, and will begin sampling in October. Pricing for the XR21B142x family of USB to serial bridge devices starts at $3.73 in 1,000 unit quantities.