Circuit and MCU Problems

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Circuit and MCU Problems [Copy link]

The attached picture shows part of the circuit for capacitor testing. There are a few things I don't understand now. I wonder if I have misunderstood the circuit.

The capacitance meter I opened and checked is the STC89C52RC with LQFP44 pin. As shown in the figure, the connection method of I/O39 and I/O40 can only be the open collector method inside the microcontroller. Now I am curious about the 2.7 ohm resistance between these two pins (because of other reasons, only the component side of the circuit board can be seen, and the other side cannot be seen). What is the use? At the same time, the oscilloscope tests the base of the transistor connected to I/O39 and I/O40, and the waveform is exactly the same. The maximum current to be discharged is only 400mA, and a single MOS can do it. There is no need to be so complicated. I don’t know if I understand this circuit correctly. I hope you can correct me.

qwqwqw2088

The copied circuit is problematic.

How to understand the sentence "The capacitance meter I opened and checked is the STC89C52RC with LQFP44 pin"

呜呼哀哉

qwqwqw2088 posted on 2021-5-5 21:09 The copied circuit is problematic. "The capacitance meter I opened and looked at is the STC89C52RC with LQFP44 pin." How do you understand this sentence?

The meter uses STC's 89C52RC microcontroller. I was curious about the connection of pins 39 and 40. There is no other possibility except open collector. There is also a 2.7 ohm resistor between these two pins. I thought it was inside the microcontroller, but there is nothing special about these two pins. I came here to ask for help and see what others think.

qwqwqw2088

You can look at the manual 89C52RC 40 pin is VCC

Pin 39 is P0.0

呜呼哀哉

qwqwqw2088 posted on 2021-5-6 09:21 You can look at the manual. Pin 40 of 89C52RC is VCC and pin 39 is P0.0

This is down, there is nothing special about pins 39 and 40, so I suspect that an external resistor of about 2.7 is indeed connected between these two pins, which just doesn't make sense.