Electrical Failure
Communication line freezes occur when a peripheral device holds a shared line low and prevents other nodes from initiating a transfer. This condition, known as bus lockup, frequently arises in two-wire serial interfaces like I2C when a master reset occurs mid-transaction. The slave node continues waiting for a clock pulse that never arrives, leaving the data line asserted and unavailable.
Communication Protocol
Standard serial operations require strict synchronization between the master clock line and the slave data line. If a noise spike on the clock line is interpreted as an extra pulse, the slave transitions to an unexpected state. The master then completes its byte transfer, but the slave remains stuck in a write state, continuing to drive the data line low.
Because the master cannot drive the data line high while the slave drives it low, the interface remains blocked.
Recovery Mechanism
Clock generation sequences resolve the deadlock by mimicking the missing pulses required by the slave. The microcontroller toggles the clock line up to nine times to force the slave to release the data line. After the slave releases the line, the controller issues a stop condition to reset the interface to its idle state.
Prevention Design
Hardware watchdogs and bus timeout circuits monitor the duration of low states to detect stalls. When the data line remains low longer than the maximum allowed packet duration, the controller activates a hardware reset pin on the slave. This action reinitializes the peripheral registers and clears the line.
