{"id":320,"date":"2023-06-28T09:40:31","date_gmt":"2023-06-28T09:40:31","guid":{"rendered":"http:\/\/localhost\/embeddedwala\/?p=320"},"modified":"2023-07-27T04:13:42","modified_gmt":"2023-07-27T04:13:42","slug":"getting-started-with-i2c-hardware-connection","status":"publish","type":"post","link":"https:\/\/embeddedwala.com\/beta\/blogs\/digital-communication\/getting-started-with-i2c-hardware-connection\/","title":{"rendered":"Getting Started with I2C: Hardware Connection"},"content":{"rendered":"\t\t
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I2C<\/strong>, or Inter-Integrated Circuit, is a well-known communication protocol utilized for linking microcontrollers and integrated circuits in embedded systems.\u00a0In order to guarantee dependable communication among devices in I2C,\u00a0hardware components<\/strong>\u00a0like resistors and capacitors perform a critical role. These components maintain signal integrity and timing accuracy, both of which are fundamental to the success of data transmission.<\/p>

Why are resistors and capacitors needed in I2C?<\/span><\/b>\u00a0<\/p>

The\u00a0I2C protocol<\/strong>\u00a0employs two signals – the\u00a0data (SDA)<\/strong>\u00a0and\u00a0clock (SCL)<\/strong>\u00a0lines – which are\u00a0open-drain (or open-collector)<\/strong>\u00a0pins. An open-drain pin uses a single transistor\/FET to connect the output pin to ground when the transistor\/FET is on, while a pull-up resistor pulls the line up to\u00a0VCC<\/strong>\u00a0when the transistor is off. This type of pin is suitable for bidirectional data buses with multiple devices initiating data transfer, as the pull-up resistor limits current and prevents a short circuit when one device attempts to place logic 1 on the line while another tries to drive logic 0.<\/p>

Standard GPIO pins, on the other hand, actively drive logic 1 and 0 on a signal without a\u00a0pull-up<\/strong>\u00a0resistor, making them unsuitable for bidirectional data transmissions as two devices driving opposite logic values could cause a short circuit and damage both devices.<\/p>

\"\"<\/p>

\u00a0<\/p>

The\u00a0capacitance<\/strong>\u00a0of the I2C bus is also an important consideration because it affects the timing and signal integrity of the communication. Capacitance can cause\u00a0signal reflections, ringing, and delays<\/strong>, leading to communication errors and data loss. Capacitors can be used to filter out noise and stabilize the voltage on the bus, improving the reliability of the communication.<\/span>\u00a0<\/p>

Resistors:<\/span><\/b>\u00a0<\/p>

I2C communication requires two\u00a0pull-up resistors<\/strong>\u00a0on the SDA (Serial Data) and SCL (Serial Clock) lines. These resistors ensure that the data lines remain in the high state when no data is being transmitted, and they provide a path for the data lines to return to the high state after a device has transmitted a low state.<\/span>\u00a0<\/p>

The formula for calculating the value of the pull-up resistor for I2C communication is:<\/span>\u00a0<\/p>

R = (Vcc\u00a0– Voh) \/\u00a0Iol\u00a0<\/strong><\/p>

where:<\/span>\u00a0<\/p>

R<\/strong>\u00a0= resistance of the pull-up resistor (in ohms)\u00a0<\/span>\u00a0<\/p>

Vcc\u00a0<\/strong>= supply voltage of the I2C bus (in volts)\u00a0<\/span>\u00a0<\/p>

Voh<\/strong>\u00a0= minimum high-level output voltage of the I2C driver (in volts)\u00a0<\/span>\u00a0<\/p>

Iol<\/strong>\u00a0= maximum sinking current of the I2C driver (in amperes)<\/span>\u00a0<\/p>

The value of Voh and\u00a0Iol\u00a0are specified in the datasheet of the I2C driver. For example, if the\u00a0Vcc\u00a0of the I2C bus is 5V, the Voh of the I2C driver is 3.3V, and the\u00a0Iol\u00a0is 3mA, then the value of the pull-up resistor can be calculated as follows:<\/span>\u00a0<\/p>

R = (5V – 3.3V) \/ 0.003A R = 566 ohms\u00a0<\/strong><\/p>

In practice, the value of the pull-up resistor is typically between 1k\u03a9 to 10k\u03a9, depending on the bus capacitance and the number of devices connected to the bus. It is important to choose the appropriate value of the pull-up resistor to ensure reliable communication between devices. If the value of the pull-up resistor is too low, it can cause excessive current flow and damage the I2C driver. If the value of the pull-up resistor is too high, it can cause signal degradation and errors in communication.<\/span>\u00a0<\/p>

Bus Capacitance:<\/span><\/b>\u00a0<\/p>

The formula for calculating the maximum allowable bus capacitance for I2C communication is:<\/span>\u00a0<\/p>

C = (Iol\u00a0\/ (dV\/dt)) * 1.2\u00a0<\/strong><\/p>

Where:<\/span>\u00a0<\/p>

C<\/strong>\u00a0= maximum allowable bus capacitance (in farads)\u00a0<\/span>\u00a0<\/p>

Iol\u00a0<\/strong>= maximum sinking current of the I2C driver (in amperes)\u00a0<\/span>\u00a0<\/p>

dV\/dt<\/strong>\u00a0= maximum allowed change in voltage per unit time (in volts\/second)<\/span>\u00a0<\/p>