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Why does my I2C clock stretch?
Clock stretching allows an I2C slave device to force the master device into a wait state. A slave device may perform clock stretching when it needs more time to manage data, such as store received data, or prepare to transmit another byte of data.
What is clock stretching?
Clock stretching is a feature in HDMI 1.3 and above. It is related to the DDC control bus and provides an explicit clock signal which relieves master and slave from synchronizing exactly to a predefined baud rate.
Does Arduino support I2C clock stretching?
Software I2C library. SoftWire is a software I2C implementation for Arduino and other Wiring-type environments. It utilises the pinMode(), digitalWrite() and digitalRead() functions. Multiple objects (for multiple software I2C buses) and clock-stretching by slave devices are supported.
Does SPI support clock stretching?
Slave devices in the SPI protocol do not use the clock stretching function; slave devices in the SPI protocol do not use the clock stretching function.
What is I2C clock speed?
The standard clock (SCL) speed for I2C up to 100KHz. Philips do define faster speeds: Fast mode, which is up to 400KHz and High Speed mode which is up to 3.4MHz. All of our modules are designed to work at up to 100KHz.
What is ultra fast speed in I2C?
Design
| Mode | Maximum speed | Direction |
|---|---|---|
| Fast mode plus (Fm+) | 1 Mbit/s | Bidirectional |
| High-speed mode (Hs) | 1.7 Mbit/s | Bidirectional |
| High-speed mode (Hs) | 3.4 Mbit/s | Bidirectional |
| Ultra-fast mode (UFm) | 5 Mbit/s | Unidirectional |
What is the maximum speed of I2C?
Data on the I2C-bus can be transferred at rates of up to 100 kbit/s in the Standard-mode, up to 400 kbit/s in the Fast-mode, up to 1 Mbit/s in Fast-mode Plus, or up to 3.4 Mbit/s in the High-speed mode. The bus capacitance limits the number of interfaces connected to the bus.
Can a clock stretching I2C device slow down SCL?
Clock Stretching I2C devices can slow down communication by stretching SCL: During an SCL low phase, any I2C device on the bus may additionally hold down SCL to prevent it from rising again, enabling it to slow down the SCL clock rate or to stop I2C communication for a while. This is also referred to as clock synchronization.
Why is clock stretching important for the I2C bus?
Clock stretching sounds a bit odd but is common practice. However, the total bandwidth of the shared bus might be significantly decreased. So, especially for I2C buses shared by multiple devices, it is important to estimate the impacts of clock stretching. So do not make the slowest I2C device dominate your bus performance.
When does an I2C slave need to slow down?
However, there are situations where an I2C slave is not able to co-operate with the clock speed given by the master and needs to slow down a little. This is done by a mechanism referred to as clock stretching. An I2C slave is allowed to hold down the clock if it needs to reduce the bus speed.
When is clock stretching allowed in high speed mode?
Clock stretching in High-Speed-Mode is only allowed after the ACK bit (and before the 1st bit of the next byte). Stretching between bits 2-9 is illegal because the edges of these bits are boosted with an additional current source. See I2C specification Rev. 03 chapter 5.3.1 for further details.