Arduino pro mini, what pins I can't use?

Hello!
Just found a very strange issue. After prototyping my project on Uno, I flashed Pro mini and nothing works.
In this project I use display with tm1637 chip connected to pins 1 and 2 (DIN & CLK). And somehow it doesn't work. Of course I have programmer disconnected from DTR, RX and TX.
Finally I used A3 instead of 1 and it seems ok now.
But again, with Arduino Uno everything works fine.

Is it defected or there are pins I can't use for certain purposes?
Will it be the same issue with Nano?

Pro Mini and Uno use the same chip and same pins. Except A6 and A7 it's identical to an Uno. Conclusion, you're doing stomething wrong / different.

PS Using Pin 1 on both an Uno and a Pro Mini can give you trouble with serial and/or programming.

Where were you making the connection for pin 1? It would be labeled TXO on the pro mini.

david_2018:
Where were you making the connection for pin 1? It would be labeled TXO on the pro mini.

Here, but now I’m not sure I’m doing it right. I thought it rx1, no?

Thank you a lot!

And another question, it all the time freezes up, can it be some issue with libraries that not compatible?
I use those:
<Wire.h>
<DS3231.h>
"OneButton.h"
<EEPROM.h>
<Arduino.h>
"TM1637.h"
Sure thing I’ll check all wiring and code, but maybe there are some known issues?

Pins 0 and 1 should not be used on an Uno or a Pro Mini because they are also used for serial. However, for some applications, and some serial adapters, they may work, assuming that you don't use Serial in your sketch - the reason being that some serial adapters put a resistor in series with the TX and RX lines, so that if they're set OUTPUT, the atmega328p will be able to overpower whatever the external serial adapter is trying to do. This is not always done on standalone serial adapters, though, and where it isn't, the two will fight over the state of the pin, typically resulting in the system not working as expected.

Add to that, depending on what you're doing, you may want there to not be series resistors, or may need them!

UrsusBear:
Here, but now I’m not sure I’m doing it right. I thought it rx1, no?

Ahh, that is a little cavat! The Pro Mini does not number those pins. And, a bit weird but okay, as on the Uno the Rx is pin 0 and Tx is pin 1. Aka, the order is misleading.

And to add to that on some clones they try to help you with the serial pins. Because it’s always a bit confusing when a pin is labeled Tx. Does that mean it’s the Tx of the device or where you connect the Tx of another device? (Okay, first is more common. ;)) This is sometimes fixed by labeling the pins TXO and RXI for Transmit Output and Receive Input. So it does not read Tx0 (zero) and Rx1 (one). Yessssss, if the team would have thought about that they would have used Tx on pin 0 and Rx on pin 1 but they did not :frowning:

But beside that, if you want to easily program the Arduino as well it’s easier to not use pin 0 and pin 1. Because a Pro Mini has no resistors in line with them aka the Serial converter connected to program it will fight with whatever is connected to pins 0 and 1 :wink:

septillion:
Yessssss, if the team would have thought about that they would have used Tx on pin 0 and Rx on pin 1 but they did not :frowning:

I think it's so that pins 0~7 correspond to port pins PD0~PD7. RX is on PD0, TX on PD1, so RX was arduino pin 0, TX arduino pin 1.