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The USBmicro U421 USB Interface

The U421 is a USB solution that is pre-built, pre-programmed, and pre-tested and will get you interfacing your PC (Win⁄Linux) or Mac (OSX) to various devices in very little time! There is no USB device assembly, no driver development, and no firmware to write. In many cases the U421 can be plugged into an experimenter's breadboard and circuit interfacing can begin immediately. Demo software applications can be used "right out of the box".


U421 top view.

Features of the U421 USB Interface

Overview of the U421 USB Interface

The U421 provides a simple digital i⁄o interface for the PC (Win⁄Linux) or Mac (OSX) . Sixteen i⁄o lines from the microcontroller are provided. Commands can be sent to the U421 that change the i⁄o lines from input to output. I⁄o lines can be individually selected as inputs or outputs. The U421 supports commands to read the ports, and if the ports are set to output, to write to the ports.

The U421 is an interface to SPI (Serial Peripheral Interface) devices. SPI is a local synchronous serial bus that uses a clock line, two data lines, and a device select line for communication between a serial device and a host microcontroller. The firmware on the U421 provides generic access to read and write SPI devices. The SPI clock rate can be adjusted to 62.5 kHz, 500 kHz, 1 MHz, or 2 MHz. Because additional pins are available as generic i⁄o, the U421 can use these lines as slave select lines and address multiple SPI devices.

The SPI subsystem of the U421 can be used as a master to communicate with SPI devices such as EEPROMS and A⁄D converters. The U421 can also be used as a SPI slave to a microcontroller that uses the U421 as a gateway to the PC (Win⁄Linux) or Mac (OSX) . A PIC, for example, can act as a SPI master to communicate data with the U421, which can then transfer the data to a PC (Win⁄Linux) or Mac (OSX) application. Most microcontrollers can communicate via SPI with software-driven routines, many have internal SPI hardware. SPI hardware is present on microcontrollers from little 8-bit devices, like the PIC, to 32-bit microcontrollers like the 680x0-based devices.

The U421 is a convenient way to interface a standard Hitachi-type of intelligent LCD controller to USB. The commands that support communication to the LCD module are the "standard" LCD commands. Standard commands include writing characters to the display, and controlling the display.

The U421 is an assembled and tested circuit card that is 1.5 inches (38.1mm) long and 0.75 inches (19.1mm) wide. The U421 is a printed circuit board in a 24-pin "DIP-like" format.

The U421 interfaces to the PC (Win⁄Linux) or Mac (OSX) via the USB port. An application on the PC (Win⁄Linux) or Mac (OSX) controls the U421. The U421 does not use any custom drivers, just the drivers that are a part of the operating system. Custom software can be developed to use the U421, or the applications that have been created as examples here can also be used.

Uses for the U421 USB Interface

With the U421 you can utilize the USB port on your computer to interface to various electronic devices, such as: lights, LCD displays, SPI analog and memory devices, switches, relays, tethered robots, model railroad control, and many custom circuits.

See the ODN U4x1 Application Notes section for examples of using the U421.

Product suitability for your particular purpose⁄use

We have made every attempt to prepare information about the products we carry so that you, as a customer, can make an informed decision to purchase or not. It is entirely at your discretion to make this decision and we do not guarantee that a product will be suitable for any particular purpose.

Hardware:  U401 USB Interface    U421 USB Interface   U451 USB Interface

Programming:  USBm DLL Programming    Download Files

Application Notes:  U4x1 Application Notes    Misc Applications and Information    FAQ

While every effort has been made to make sure that the information posted on this site is correct, the author can not be held liable for any damages whatsoever for losses as a result of the application of this information. Use this information at your own risk.

USBmicro can design your custom and semi-custom USB product. Email about USB design can be directed to " Robert " at

Copyright © USBmicro, L.L.C., 2002-2010

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