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Author Topic: TX and RX always HIGH  (Read 423 times)
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Hello,

One offered me an Arduino at Christmas.
I made my first step with it and understood the basics.
Today, i try to make it communicate via FBus with a Nokia (few or false documentation on this ... another problem).

And I noticed some unexpected voltage. Here is a summary:
- Arduino UNO rev 3
- Program loaded : blink example
- Measurement :
                   voltage between ground and TX pin : 4.6 V
                   voltage between ground and RX pin : 4.9 V
- LEDs : RX and TX are off

Is this normal ?
I mean, in serial communication, does a HIGH value is expected when nothing is communicated ?

Thank you for your help, I will come with many more question after that I guess !

Loïc
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Hello,

One offered me an Arduino at Christmas.
I made my first step with it and understood the basics.
Today, i try to make it communicate via FBus with a Nokia (few or false documentation on this ... another problem).

And I noticed some unexpected voltage. Here is a summary:
- Arduino UNO rev 3
- Program loaded : blink example
- Measurement :
                   voltage between ground and TX pin : 4.6 V
                   voltage between ground and RX pin : 4.9 V
- LEDs : RX and TX are off

Is this normal ?
I mean, in serial communication, does a HIGH value is expected when nothing is communicated ?
Yes, that is the so called 'stop condition' for TTL level serial communications.

Thank you for your help, I will come with many more question after that I guess !

Loïc

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normal, unless it's transmitting then it will read close to 0v.

(i presume the trans/recv pins are inverted to light up the LED's)
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Fast & efficient !
Thanks to both of you !

I'll keep this in mind from now !

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Wonderful and easy Arduino tutos here : ThePolyscope.com
And also science new and various tech topics !

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