Notice the two pull-up resistors on the two communication lines. Resistor selection varies with devices on the bus, but a good rule of thumb is to start
with 4.7kΩ resistor and adjust down if necessary
. I
2
C is a fairly robust protocol, and can be used with short runs of wire (2-3m).
Does I2C need pullup resistors?
The I2C bus must have
pull-up resistors
, one on the SDA line and one on the SCL line. They’re typically 4.7K or 10K ohm, but should be in the range of 2K to 10K.
What pull-up resistor do I need?
Pull-up resistors are used to solve the dilemma for the microcontroller by
pulling the value to a logical high state
, as seen in the follow figure. Without the pull-up resistor, the MCU’s input would be floating when the switch is open and pulled down to a logical low only when the switch is closed.
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 do you find the pull-up resistor value?
First, use IEN, ILKG, and Equation 1 to find the current through the pull-up resistor, IPull-up. Now that IPull-up has been calculated, the maximum value for RPull-up is found by using Equation 2. An output voltage, Vout, of 1.8 V is used as an example. The next step is to find the minimum pull-up resistor value.
How many slaves can be connected in I2C?
i2c in particular is a great bus mechanism, due to the microprocessor only needing TWO wires to control (almost) any number of devices. 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.
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.
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.
What does a 10K ohm resistor look like?
What does a 10K ohm resistor look like? A 10k ohm resistor has
4 color bands: brown, black, orange, and gold for 5% tolerance
, respectively. A 1k ohm resistor has 4 color bands: brown, black, red, and gold for 5% tolerance, respectively.
Why does Port 0 needs pull up resistors?
An external pull-up resistor is needed when Port 0
is defined as an output port
. Port 0 of the 8051 has two main functions: To be used as a simple input-output port and to access external memory in conjunction with Port 2.
What is the speed for fast mode in I2C?
| Wires 2 (SCL and SDA) | Data Frame Size 8 Bits packets | Maximum speed Standard mode = 100 Kbps | Fast Mode = 400 Kbps | High-Speed mode = 3.4 Mbps |
|---|
Does SPI need pullup resistors?
For the SPI operation
no pull-ups are needed
. Unlike the I2C where pull-ups are needed because the drivers have open collector outputs, no pullups are needed on the SPI signal lines since the drivers have push-pull outputs.
How do you calculate the I2C pullup resistor?
These pull-ups would draw 3.3V / 1.77 k =
1.86 mA
each when SCL / SDA is low. So, theoretically, if this bus has the absolute maximum amount of capacitance on it, this bus should use at least 1.77 k Ohm pull-up resistors, down to 171 Ohm resistors if their maximum low drive strength is 13.5 mA each during SCL/SDA low.
Why pull up resistors are used 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
.
What is the difference between pull up and pull-down resistor?
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.
How many external pull up resistors are used in port 0?
Full Member level
5
. Pull-ups are used so that components with a different driving voltage can be connected to the microcontroller.
