write data to a register using wire library

Thus, after the I2C address, the register address may follow. I2C devices typically have multiple registers with their own addresses. During transmission by the master device, the I2C address goes out first.

There is no slave select (SS) line, so I2C devices each have their own addresses to identify them. A stop condition occurs when the SDA goes high after SCL.

The stop condition signals the end of transmission. Data goes out immediately following the start condition. A start condition occurs when the SDA goes low before the SCL. The image below (click to enlarge) best describes the protocol:īoth SDA and SCL lines are high when idle. I2C, however, is a more complex protocol. SPI is simple enough that you can implement it through bit-banging or use shift registers to read its data. But a 5V I2C sensor will not work with a 3.3V microcontroller. For example, it’s OK to connect a 3.3V I2C sensor to a 5V arduino because the latter can still read 3.3V. This allows devices with different operating voltages to be usable but only if the lower voltage is still readable by the higher-voltage device. Bus devices pull-down the voltage on the bus instead of using their own operating voltage. Having pull-up resistors is an open-drain scheme. If you don’t want to bother calculating the resistor value, use the typical 4.7 kΩ. Where V OL is the logic low voltage, I OL the logic low current, t r is the maximum rise time of the signal and C b is the bus (wire) capacitance. Texas Instruments recommends the following formulas to calculate the correct pull-up resistor value:

The pull-up resistor value depend on a number of factors. These two bidirectional lines have pull-up resistors. SDA is short for Serial Data Line and SCL is short for Serial Clock Line. The I2C protocol requires only an SDA and SCL pin. And while SPI is the fastest out of the three, speed isn’t everything. However, SPI needs at least four pins (MOSI, MISO, SCK, SS) and doesn’t support multiple masters. Moreover, the additional two-bits (start and stop) used in UART transmission adds overhead and thus wastes a part of the data rate.īoth SPI and I2C are capable of one-is-to-many transmission. Asynchronous serial protocols like RS-232 (UART) is for one-is-to-one communication only.

Write data to a register using wire library