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Photo of USB-I2C/IO Rev. B board
USB I2C/IO P.C.B. (Rev. B)

What's the same?

The Rev. B board is nearly identical to the Rev. A board in both form factor and function. It was our intention that the board would be as close to a "drop-in" replacement for the Rev. A boards as possible.

Physical Dimensions (2.25" X 3.0").
Location and size of mounting holes (0.150" from edges, 0.125 diameter hole).
Physical location of connectors and signals for USB-B, Debug, and I2C connectors.
Physical location of 24 of the 26 signals originally on the 26 pin header (Rev. A boards).

What's different?

The Rev. B board has been enhanced in an effort to provide more features and some additional protection.

It's Blue! The Rev. B board uses Blue Solder Mask to make it easy to distinquish between Rev. A and Rev. B boards.
Eliminated one of the ground test points.
Moved all test points to edge of board for easier access.
Changed regulator circuit capacitors to better comply with component datasheet and USB specification.
Added Ferrite Beads to Vusb and Ground signals from USB connector (EMI filtering).
Added ESD protection device to USB D+/D- and I2C SCL/SDA signals (ESD hardening)
Added resettable fuse to Vusb signal to provide some protection for upstream equipment. This fuse goes to high impedance state in an overcurrent condition, and automatically returns to low impedance state when it cools.
Added write protection for I2C eeprom. The write protection can be enabled or disabled via a jumper.
Changed eeprom enable jumper from a 2 pin to a 4 pin header, to include write protect feature.
Added pullup resistor for I2C interrupt signal.
Changed "Status" LED to surface mount component.
Added "Breakpoint" LED to show state of "Breakpoint" signal from AN2131QC.
Changed P.C.B. footprint and schematic pinout for the two 5 pin headers (Debug and I2C). The signals are all still in the same physical locations as the Rev. A board, only the references to pin numbering have been changed (to match the actual AMP reference on the mating connector). In other words, pin 1 is now pin 5... but pin 5 is where pin 1 used to be... and has the same signal on it.
Increased I/O connector from 26 to 34 pins. The 34 pin connector is exactly 8 pins larger, and is situated such that the center 26 pins occupy the same physical space as the orignal 26 pin header (4 extra pins on each end). All but two of the original I/O signals are in their exact same physical space. The I2C signals have been replaced with CLK24 and RESET, and the additional 8 pins are for the data bus signals. This change provides support for the "Fast FIFO Transfer" operations of the AN2131QC, which will allow the board to transfer data to/from external circuitry at full USB 1.1 rates (nearly 1MB/sec on an unloaded bus).


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Last modified: August 25, 2008