TX and RX always HIGH

Using Arduino IDE 1.x
1

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

2

Loic_B:
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

3

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)

4

Fast & efficient !
Thanks to both of you !

I'll keep this in mind from now !