OLIMEX© 2017
OLIMEXINO-32U4 user's manual
CHAPTER 6 CONTROL CIRCUITY
6. Introduction to the chapter
Here you can find information about reset circuit, power circuit and quartz crystal locations.
6.1 Reset
OLIMEXINO-32U4 reset circuit includes R7 (4.7kΩ), R8 (330Ω), D1 (Shottky diode),
ATmega32U4 pin 13 (#RESET) and a RESET button. Note that it also can be found at the ICSP
header pin 5 and power connector pin 1.
6.2 Clock
16MHz quartz crystal Q1 is found at pins 16 and 17 of the processor.
By default OLIMEXINO-32U4 operates at 5V, which allows the main microcontroller
(ATmega32u4) to operate properly at the maximum clock speed (16 MHz). The ATmega32u4
would work properly at 16MHz only if powered by at least 4.5V.
If you decide to change the position of the jumper 3.3V/5V jumper to 3.3V position, please note
that, at 3.3V, the maximum frequency that can be achieved with ATmega32u4 is around 10MHz,
thus the 16MHz operation is a significant overclock. Yet, our tests proved that the board works
reliably with a 16MHz quartz even at 3.3V.
IMPORTANT: If the board has a quartz crystal rotated at 45 degrees relative to the pads provided
do not panic. This is normal. We have two types of such crystals – one of them requires 4 pads, the
other only 2 pads. That is why we have provided 4 pads to be able to fit both crystals. All boards
Olimex manufactures pass automatized optical inspection after assembly and obvious misplacement
like this is impossible to occur.
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