May I use both USB-serial and tx/rx pins at the same time?

Question

I am building a CNC machine based on GRBL code on a uno. I also have found a script to read data on a N64 controller. I know there is not enough pins available to do both codes running on the same arduino, so I was wondering if I could have my GRBL arduino connected to a computer thru USB, and at the same time, have a second arduino reading data from the n64 joystick, create Gcode accordingly, and feed that Gcode to the GRBL arduino through the tx/rx pins of each of them. I guess I'll have to put a on-off switch on the tx/rx wife to avoid "noise" when I actually send Gcode to the GRBL arduino from the computer.

Does this all make sense?

Answer 1

The usb port and the tx/rx pins are one and the same thing. You can't use one thing for two jobs at the same time. So you will either have to implement some kind of multiplexing system (switches) or come up with a different way of doing things, maybe using the SoftwareSerial library or the Wire Library or investing in a better board with more than one serial port.

Answer 2

Low impedance circuits connected to the TX/RX pins would cause distortion in the serial signal and would interfere with communication.

A switch would help here. Alternately, you could use a Mega 2560 with more IOs, or if you are breadboarding it, use a 1284p chip.

You could also use SoftwareSerial to communicate with the other Arduino on another set of pins.