SPRUJ17I March 2022 – August 2025 AM2631 , AM2631-Q1 , AM2632 , AM2632-Q1 , AM2634 , AM2634-Q1
Under normal conditions only one controller device generates the clock signal; the SCL. During the arbitration procedure, however, there are two or more controller devices and the clock must be synchronized so that the data output can be compared. Figure 13-16 illustrates clock synchronization. The wired-AND property of the SCL line means that a device that first generates a low period on the SCL overrules the other devices. At this high-to-low transition, the clock generators of the other devices are forced to start their own low period. The SCL line is held low by the device with the longest low period. The other devices that finish their low periods must wait for the SCL line to be released before starting their high periods. A synchronized signal on the SCL is obtained where the slowest device determines the length of the low period and the fastest device determines the length of the high period.
If a device pulls down the clock line for a longer time, the result is that all clock generators must enter the wait state. In this way, a peripheral slows down a fast controller and the slow device creates enough time to store a received byte or to prepare a byte to be transmitted.
I2C Protocol Fault
The following conditions violate the clock spec as defined in the Philips I2C bus specification, v2.1 (The I2C Specification, Philips document number 9398 393 40011), and will result in an I2C protocol fault: I2CCLKH = 2, I2CCLKL = 2, I2CPSC = 2. This will cause the SDA data transition to occur while the SCL is high.
Figure 13-16 Synchronization of Two I2C
Clock Generators During Arbitration