Difference between revisions of "I²C"

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The {{I2C}} bus consists of two data signals, one clock and one bi-directional data line.  One master and multiple slaves can be connected in parallel to the same bus.  The signal pins of all devices are so-called open-drain, meaning they will never supply a voltage to the signal line but either be shorted to GND or in high-impedance mode.  For that reason, both clock and data will need to be pulled high by a resistor.  The benefit of this approach is that if multiple slaves respond simultaneously they never risk frying each other.  The size of the pull-up resistor depends on the application.  On a very short bus (5-10 cm tops) with only one mater and one slave, the resistor can be quite big (read: internal pull-up in a {{STM32}} {{MCU}} will do just fine).  This is known as a weak pull-up.  On a longer bus or a bus with more devices, a stronger pull-up is needed, meaning a smaller resistor.  4.7K to 10K is common.
 
The {{I2C}} bus consists of two data signals, one clock and one bi-directional data line.  One master and multiple slaves can be connected in parallel to the same bus.  The signal pins of all devices are so-called open-drain, meaning they will never supply a voltage to the signal line but either be shorted to GND or in high-impedance mode.  For that reason, both clock and data will need to be pulled high by a resistor.  The benefit of this approach is that if multiple slaves respond simultaneously they never risk frying each other.  The size of the pull-up resistor depends on the application.  On a very short bus (5-10 cm tops) with only one mater and one slave, the resistor can be quite big (read: internal pull-up in a {{STM32}} {{MCU}} will do just fine).  This is known as a weak pull-up.  On a longer bus or a bus with more devices, a stronger pull-up is needed, meaning a smaller resistor.  4.7K to 10K is common.
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== {{I2C}} Addresses ==
 +
 +
{| class="wikitable"
 +
!Field:
 +
!S
 +
| colspan="7" |I<sup>2</sup>C address field
 +
|R/W'
 +
|A
 +
|I<sup>2</sup>C message sequences...
 +
|P
 +
|-
 +
!Type
 +
! rowspan="5" |Start
 +
! colspan="8" |Byte 1
 +
! rowspan="5" |ACK
 +
! rowspan="5" |Byte X, etc.
 +
Rest of the read or write
 +
 +
message goes here
 +
! rowspan="5" |Stop
 +
|-
 +
!Bit position in byte X
 +
!7
 +
!6
 +
!5
 +
!4
 +
!3
 +
!2
 +
!1
 +
!0
 +
|-
 +
!7-bit address pos
 +
!7
 +
!6
 +
!5
 +
!4
 +
!3
 +
!2
 +
!1
 +
|-
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| rowspan="2" |Note
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| rowspan="2" |MSB
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| colspan="5" rowspan="2" |
 +
| rowspan="2" |LSB
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|1 = Read
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|-
 +
|0 = Write
 +
|}
 +
  
 
[[File:I2C-Interface.png|600px]]
 
[[File:I2C-Interface.png|600px]]

Revision as of 03:40, 7 October 2024

I²C stands for Inter-Integrated Circuit and is pronounced I-squared-C or I-to-C. It is a synchronious multi-master, multi-slave serial communication bus invented in 1982 by Philips Semiconductors.

The I²C Bus

The I²C bus consists of two data signals, one clock and one bi-directional data line. One master and multiple slaves can be connected in parallel to the same bus. The signal pins of all devices are so-called open-drain, meaning they will never supply a voltage to the signal line but either be shorted to GND or in high-impedance mode. For that reason, both clock and data will need to be pulled high by a resistor. The benefit of this approach is that if multiple slaves respond simultaneously they never risk frying each other. The size of the pull-up resistor depends on the application. On a very short bus (5-10 cm tops) with only one mater and one slave, the resistor can be quite big (read: internal pull-up in a Template:STM32 Template:MCU will do just fine). This is known as a weak pull-up. On a longer bus or a bus with more devices, a stronger pull-up is needed, meaning a smaller resistor. 4.7K to 10K is common.

I²C Addresses

Field: S I2C address field R/W' A I2C message sequences... P
Type Start Byte 1 ACK Byte X, etc.

Rest of the read or write

message goes here

Stop
Bit position in byte X 7 6 5 4 3 2 1 0
7-bit address pos 7 6 5 4 3 2 1
Note MSB LSB 1 = Read
0 = Write


I2C-Interface.png

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