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The current sensor line to the microcontroller is an input (to the microcontroller). The output of the current sensor also goes to a comparator. As soon as the voltage output of the current sensor goes above the special trip point that corresponds to the maximum current, the output of the lm293 (or 393) changes from high to low. That causes the nands to latch into a state that gives a high output to the mosfet driver (which is OFF). The only way to clear the overcurrent fault state is to bring the "clear" pin low and then high again. As soon as the pin goes high, the nand latch is cleared and things go back to normal. The default setting in software is to clear the nand latch at about 4kHz. It's probably safer not to clear it at all, but you don't want to be driving down the freeway and all of a sudden, the car turns off for no reason other than a single spurious overcurrent event.
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