The BlueberryE Uno335 is a Arduino Uno R3 derivate adding optional levelshifters for SPI and I2C as well as 512kBit serial SRAM. All this features are controlled by jumpers to be swiched on or off. Using the right jumper settings the Uno335 is fully compatible with the Arduino Uno.
The Uno335 is an Arduino Uno R3 derivate (same pinout) and as the 335 suggests it contaisn levelshifters from 3.3 to 5V for I2C and SPI. For the two I2C the classical circuit described by Philips is used and for SPI levelshifting is accomplished by a TXB0104 from TI.
There is also a serial SRAM chip on board (512kbit) that is connected through SPI. You can find a library and some examples on the Uno335 repository on GitHub.
The following graphic show you the relevant jumpers and pins.
For I2C only the two pins close to the reset button are shifted, on A4, A5 you always can connect to the original I2C bus. The jumpers close to the power/GND pins (the 4 left ones) decide whether level shifting for I2C to 3.3V (including pull ups) is enabled. If they are set like in the drawing means levelshift is enabled.
For SPI; if you want to do level shifting always the TXB0104 must be enabled. Now pins 10,11, 12, 13 are shifted down to 3.3V. If the jumpers are set like in the drawing levelshifting is enabled.
The Serial SRAM, as mentioned earlier, has also an SPI interface but pin 10 is forseen as CS for an external SPI device. Therefore pin A3 is used as CS for the serial SRAM. The voltage level of pin A3 is brought down to 3.3V using a resistive voltage divider. If this jumper is open pin A3 can be used as usual.
Main MCU is the ATmega 328P you find something there.