What is the difference between the diode mode and the on/off mode of a multimeter?

The first gear is mainly used to measure the forward voltage drop of the diode, while the buzzer gear, also known as the on-off gear, is mainly used to measure the on-off status of the circuit. Some multimeters combine the buzzer gear and the diode gear together, while some multimeters separate these two gears.

The diode block mainly generates a voltage source of about 2.8V inside the A/D converter, which is added to the vω hole and the com hole. When you connect the red and black test leads to both ends of the diode under test, it is mainly this 2.8V voltage source that measures the forward and reverse conduction voltage drop of the diode.

The on-off position mainly relies on the operational amplifier to control the sound of the buzzer. If the resistance of the measured loop is lower than 70 ohms, sometimes it is 60 ohms. This resistance depends on the threshold of the operational amplifier. That is to say, we change the sound threshold of the operational amplifier to change the resistance of the buzzer. For example, we can make it sound at 50 ohms.