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The bit counter counts the number of sampled bits and sets the USI interrupt flag USIIFG when the USICNTx value becomes zero, either by decrementing or by directly writing zero to the USICNTx bits
I2C:
USIIFG is set when USICNTx becomes zero, either by counting or by directly writing 0 to the USICNTx bits. USIIFG is cleared by writing a value > 0 to the USICNTx bits when USIIFGCC = 0, or directly bysoftware.
USISTTIFG is set when a START condition is detected. The USISTTIFG flag must be cleared by software.
The bit counter counts the number of sampled bits and sets the USI interrupt flag USIIFG when the USICNTx value becomes zero, either by decrementing or by directly writing zero to the USICNTx bits.
当USICNTx递减为0或者直接写入0时会置位USIIFG
Writing USICNTx with a value > 0 automatically clears USIIFG when USIIFGCC = 0, otherwise USIIFG is not affected.
