A000066 Arduino, A000066 Datasheet - Page 4

• Manufacturer Part Number: A000066
• Description: Development Boards & Kits - AVR ARDUINO UNO REV 3
• Manufacturer: Arduino

Specifications of A000066

• Rohs: yes
• Product: Development Kits
• Tool Is For Evaluation Of: ATmega328P
• Core: AVR8
• Interface Type: I2C, ICSP, SPI, USB
• Data Bus Width: 8 bit
• For Use With: ATmega

be well-coordinated with the start of the upload.
This setup has other implications. When the Uno is connected to either a computer running Mac OS X or Linux, it resets each time a
connection is made to it from software (via USB). For the following half-second or so, the bootloader is running on the Uno. While it
is programmed to ignore malformed data (i.e. anything besides an upload of new code), it will intercept the first few bytes of data
sent to the board after a connection is opened. If a sketch running on the board receives one-time configuration or other data when
it first starts, make sure that the software with which it communicates waits a second after opening the connection and before
sending this data.
The Uno contains a trace that can be cut to disable the auto-reset. The pads on either side of the trace can be soldered together to
re-enable it. It's labeled "RESET-EN". You may also be able to disable the auto-reset by connecting a 110 ohm resistor from 5V to
the reset line; see
this forum thread
for details.
USB Overcurrent Protection
The Arduino Uno has a resettable polyfuse that protects your computer's USB ports from shorts and overcurrent. Although most
computers provide their own internal protection, the fuse provides an extra layer of protection. If more than 500 mA is applied to
the USB port, the fuse will automatically break the connection until the short or overload is removed.
Physical Characteristics
The maximum length and width of the Uno PCB are 2.7 and 2.1 inches respectively, with the USB connector and power jack
extending beyond the former dimension. Four screw holes allow the board to be attached to a surface or case. Note that the
distance between digital pins 7 and 8 is 160 mil (0.16"), not an even multiple of the 100 mil spacing of the other pins.