Arbitration is lost in the following circumstances:

SDA sampled as a low when the master drives a high during an address or data transmit cycle.

SDA sampled as a low when the master drives a high during the acknowledge bit of a data receive cycle.

A start cycle is attempted when the bus is busy.

A repeated start cycle is requested in slave mode.

A stop condition is detected when the master did not request it.

This bit must be cleared by software writing a 1 to it.

MCF51QE128 MCU Series Reference Manual, Rev. 3

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Freescale Semiconductor

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Freescale Semiconductor MCF51QE128RM manual Freescale Semiconductor