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 Access 1-wire temperature sensors, memory and other chips. 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 The LCD module Im using is a generic 16x2. 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: Libraries are ready-mode codes that you just need to include in your Arduino sketch in order for your LCD to work. TWCR = _BV(TWEN) | _BV(TWIE) | _BV(TWEA) enable twi module, acks, and twi interrupt It is 72 for a 16mhz Wiring board with 100kHz TWI */ Note: TWBR should be 10 or higher for master mode For the Sam3x, it expects you to set the stop bit in the control register before you send the last read command (33.8. SCL Frequency = CPU Clock Frequency / (16 + (2 * TWBR)) ardnewbie: Although the program flow for i2c is similar with AVRs TWI, there is one big difference in the order that registers get set.
* 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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