![]() ![]() I have external pullups on the bus and several I2C devices that I want to toggle their powers, but was wondering if I need to turn off the internal pullup so I don't power some I2C devices through the bus when I power them down. ![]() The internal pull-ups can in some systems To the SCL and SDA pins, as explained in the I/O Port section. Note that the internal pull-ups in the AVR pads can be enabled by setting the PORT bits corresponding So when the I2C hardware is working, does it not alter internal pullup state? This blurb from the data sheet seems to support my assumption: TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) What are the I2C Registers in Arduino What are the I2C Registers in AVR ATmega328p Which AVR Registers control and configures I2C / TWI / Two Wire Interface What is the function of the AVR I2C Registers TWBR TWI Bit Rate Register Bits 70 TWI Bit Rate Register TWBR selects the division factor for the bit rate generator. enable twi module, acks, and twi interrupt ![]() It is 72 for a 16mhz Wiring board with 100kHz TWI */ C:UsersEnder WigginDocuments on Windows 7 or. Note: TWBR should be 10 or higher for master mode For Arduino installations, this defaults to /Arduino/Libraries inside your main documents/personal folder (e.g. SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR)) * twi bit rate formula from atmega128 manual pg 204 In Wire library (or twi), the internal pullup resistors are enabled in begin(). I'm wondering how the I2C bus works with internal pullup resistors. ![]()
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