MCLR resistor

william chan

The SX manual recommends a 10K resistor to pull up the MCLR pin to 5v.
My question is, can the MCLR pin be directly be connected to 5V without any resistors?
What will be the current flow into the MCLR pin?

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SamTheMan

I think because I did it before, Yes you can connect MCLR to 5v with no problem but you will lose the ability to reset your SX without causing a short circuit.

By other words, the 10k resistor give you the ability to reset the SX with an external switch connected to GND

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Guenther Daubach

William,

the SX datasheet specifies the absolute maximum voltage applied to any input as Vdd + 0.6 Volt. Inside the SX, there are clamping diodes to protect the inputs from overvoltage. So a resistor in series with an input, like a 10 kOhm between MCLR/ and Vdd mainly protects the claming diodes in case of an overvoltage on the input. The resistor limits the current flowing through these diodes. You may use a smaller value, say down to 470 Ohm.

BTW, especially when building prototypes, it is a good idea to put 470 Ohm resistors in series with all port input pins as well, for the same reason.

Added: When posting my answer, I noticed the answer from SamTheMan - this is another good reason.

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Greetings from Germany,

G