In the MCU test function, the first thing to be tested is the OS test. The principle is that by adding a forward voltage (weak driving capability) between the GND pad and the IO pin of the chip, a voltage of 0.5~0.6V will be observed between the GND and IO PAD, indicating that the OS is normal.
In the CP stage, when we conduct OS tests on chips, only two pins of chips are connected, namely GND and IO_PAD. In this way, the test result is the voltage drop of GND and IO_PAD, which must be accurate.
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