MCLR Voltage Question

Electronegativity

Hi all, I am putting together an SX project that will have both 5V and 3.3V components.
The SX will be running at 5V because I am going to clock it fast.
It happens that it would be easier to pull up MCLR with 3.3V for layout reasons.

Will this work?
Can I pull up MCLR with 3.3V when the SX is running on 5V?

Thanks.

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I wonder if this wire is hot...

Guenther Daubach

Electronegativity,

the SX datasheet's DC characteristics section specifies for the MCLR*, OSC1, and RTCC pins the logic high level as 0.8*Vdd (min), and the logic low level as 0.2*Vdd (max). When you run the SX at 5V, the minimum for high level is 4V, and the maximum for low level is 1V. So if the datasheet is right, you would have problems pulling up MCLR* to 3.3V only.

You mentioned that you are going to clock the SX fast - do you mean over 50 MHz? In case you don't go beyond 50 MHz, the SX would work fine at 3.3V, so you would not need a separate 5V supply for the SX.

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Greetings from Germany,

G

Electronegativity

Thanks Guenther, I am probably going to use a 50 MHz crystal, so that sounds like a good idea.

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I wonder if this wire is hot...