Does I2C need pullup resistors?

I2C communication standard is the mostly widely used inter-chip communication standard in today’s electronic systems. Pullup resistors need to be connected from the I2C lines to the supply to enable communication as shown in Figure 1.

How do you tell if a resistor is pull up or pull down?

A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.

What happens if the pull-up resistor for an I2C signal is too small?

There are now additional restrictions on the range of pull-up resistors; the pull-up value will form an RC circuit with the bus capacitance. Too small of a value will once again prevent the output drivers from sinking enough current to pull the pin all the way down to 0.

Why pull-up resistor is required in I2C?

As discussed in the I2C Basics module, the resistors that are commonly seen on I2C circuits sitting between the SCL and SDA lines and the voltage source are called pull up resistors. A pull up resistor is used to provide a default state for a signal line or general purpose input/ouput (GPIO) pin.

How many slaves can be connected in I2C?

Each device on an i2c network has a 7-bit address, so a single network theoretically supports up to 128 slave devices.In practice though, the limit is much lower. i2c slave chips often support only 8 different bus addresses, no more than 8 of that chip can be attached to the same i2c network.

Why do you need pull-up resistors?

In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. A pull-up resistor effectively establishes an additional loop over the critical components, ensuring that the voltage is well-defined even when the switch is open.

How do you calculate pull-down resistors?

To calculate the pull-down resistor value, it’s slightly different from the pull-up resistor value. Knowing that current is 100uA, we’ll take 0.5v as our pull-down voltage since the input is 0.8v. Thus, applying our R = V/I once again, but this time we don’t have to minus, so our formula remains constant.

Why do you need pull up resistors?

What happens if the pull-up resistor for an i2c signal is too large?

If your pull-up resistor is too large, then it won’t be able to overcome the leakage current. If it just barely overcomes the leakage current, then any noise in the circuit could be enough to change the input.

How many pull-up resistors for I2C?

I2C Current Specifications and Bitrates The I2C specification allows a maximum of 3 mA pull-up current on each I2C line. The Aardvark adapter has two internal pull-up resistors on each line: 2.2k ohm and 100k ohm resistors in parallel. The 2.2k ohm resistor can be turned on and off.

Is there a correct resistance value for I2C pull-up?

The SDA bus requires a pull-up resistor to VCC (typical 10 kΩ for 100 kHz, 2 kΩ for 400 kHz and 1 MHz). I thought that any resistor with a kΩ value would do the job (and it seems that my EEPROM works fine at different frequencies with a 10 kΩ resistor).

What’s the rise time of an I2C resistor?

On I2C/TWI with resistive pull-up and nominal trace capacitance, rise times can be 5-10ns. Fall times are a bit faster since it is an open-drain transistor pulling down instead of a resistor pulling up. 4. For that hypothetical 2 foot line, the echo will come back during the rise time, and will be swamped by the RC of the line.

When do pull up resistors pull the line high?

The pullup resistors pull the line high when it is not driven low by the open-drain interface. The value of the pullup resistor is an important design consideration for I2C systems as an incorrect value can lead to signal loss.

Where are the terminating resistors for I2C / Twi?

There terminating resistors (somewhere around 120 ohms as I recall) are very much in order. But, for I2C/TWI, its a whole different ball game. You CAN put those resistors anywhere on the line and in the very large proportion of cases, there will be virtually no consequence.