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Electronics -- USB 8bit Interface Board

A small and easy-to-use 8bit parallel interface for the USB.

Overview

Rev. 4 SMD image (top) [8kb]
[click to enlarge: 117kb JPEG]

This is a USB (universal serial bus) interface board which can be used to connect 8 (parallel) data lines to the USB. The interface comes with a small internal FIFO (384 byte Tx, 128 bytes Rx) and 4 handshake lines which make it suitable for interfacing microcontroller designs to the USB.

It can, also be used as simple 8bit IO when the so-called "bitbang mode" is enabled. Note. however, that in this mode, the bits will not come out in a constant bitrate but in chunks of 64 bytes with specified baud rate followed by a delay.

If you are after throughput (i.e. more than 800kb/s), then have a look at USB-FX2, a USB-2.0 "high speed" board.

Schematic

Rev. 4 SMD image (bottom) [9kb]
[click to enlarge: 150kb JPEG]

The circuit is held as small as possible while still retaining the required features:

  • Allows USB-powered and self-powered operation.
  • Configuration EEPROM, power LED.
  • Connectors for all handshake/control lines (although usually only 4 out of 7 are needed).
  • Direct flip-mounting on microcontroller board.

Have a look at the complete schematic.

Software Support

Clearly, some software had to be written to test the device. And of course, it had to run under Linux...
Fortunately, one does not have to develop all the necessary things oneself since the Linux kernel comes with support for USB-to-serial converters based on this chip and FTDI offers an interface library (libftdi) dedicated to their chips.

Furthermore, some utility to write/change the configuration EEPROM contents is needed for convenience. It turns out that this can easily be done from the USB port.

More information and source code can be found on the software page.


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Last modified: 2006-08-19 14:46:47