Can you pull TX pin to GND?

Hello,
I'm working on a Nixie Tube project of mine. I've used all of my pins except D0(TX),D1(RX), A6 and A7. The goal right now is to turn the nixie tubes on with motion detection. The cheapest and most available motion detector I could find is the HC-SR501

The High Voltage power supply I am using has a feature that enables the PS to turn OFF when given logic HIGH. I was thinking I would use pin A6 to read the state of the PIR M.D., and use pin D0(TX) control the state of the power supply.

My concern is that the power supply pulls its on/off pin to GND, so if I connect the arduino's TX pin to this power supply's on/off pin, the arduino's TX pin will be pulled to GND as well.

I don't think this will be an issue, as the only time the TX pin is used is when I upload code and the arduino begins to run. During this time, the high voltage power supply that I am speaking of is not powered by an external 12v. Am I mistaken though?

From what I understand, the only reason I would ever need a TX pin is to receive serial data on the computer, of which I am not using because this project does not make the use of the serial ports for anything except upload. I hope this made sense, thank you for your time!

Pins 0 and 1 can be used as regular I/O pins if you don’t need serial communication. If you want to pull a pin to GND it must be set as INPUT or INPUT_PULLUP. When the Tx pin is used for Serial it will be set as OUTPUT and in that case you should NOT pull it to GND.

If you do connect something to pins 0 and 1 for regular I/O purposes you will probably need to disconnect it before uploading a program.

…R

Robin2:
When the Tx pin is used for Serial it will be set as OUTPUT and in that case you should NOT pull it to GND.

If you do connect something to pins 0 and 1 for regular I/O purposes you will probably need to disconnect it before uploading a program.

...R

Is it okay to pull it to GND externally and then upload code?

Rocky_arduino:
My concern is that the power supply pulls its on/off pin to GND, so if I connect the arduino's TX pin to this power supply's on/off pin, the arduino's TX pin will be pulled to GND as well.

If this is an input control signal to the high voltage power supply, I would expect "pulls its on/off pin to GND" means that there is a moderately high value resistor to GND such that the power supply will default to On if the input is not driven. If this is the case, then it won't bother the Arduino TX pin even if it is configured as an output. The Arduino could be programmed, but the hazard would be that the high voltage power supply would be switched On/Off with whatever is going on the Tx pin during programming and/or the bootloader process.

We'd have to know the specific characteristics of the On/Off pin of your particular power supply to be certain.

Rocky_arduino:
Is it okay to pull it to GND externally and then upload code?

What part of the word "NOT" is causing a problem?

And the Tx pin is used as part of the upload process so it can't be tied up or down - even if doing so would not cause damage.

...R