Question

In an I2C multi-master configuration, what is the exact function of clock stretching when a slave device requires more time to process data than the master&#x27;s current clock speed provides?

Accepted Answer

In an I2C bus, the master device dictates the timing by toggling the Serial Clock (SCL) line. Clock stretching is a mechanism where a slave device physically holds the SCL line at a logic low level after receiving or sending a byte, effectively pausing the communication. Because the I2C bus uses an open-drain configuration—where devices only pull the line low and let resistors pull it high—a slave can force the clock to remain low even if the master attempts to pull it high. The master is required to monitor the SCL line after releasing it for a high signal; if the master detects that the SCL line is still being held low by the slave, it must wait and stop sending further clock pulses. This delay gives the slave additional time to perform internal operations, such as completing a measurement or processing a data buffer, before it is ready to receive or transmit the next bit. Once the slave finishes its task, it releases the SCL line. Because the SCL line is connected to a pull-up resistor, it will naturally transition to a logic high state. Upon detecting this transition, the master resumes the clock signal and proceeds with the transaction. Clock stretching ensures synchronization between master and slave devices operating at different speeds, preventing data loss that would occur if the master attempted to read or write data before the slave was ready.

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In an I2C multi-master configuration, what is the exact function of clock stretching when a slave device requires more time to process data than the master's current clock speed provides?