Connections to Nano for SPI and Serial Port

Official Hardware Nano Family Classic Nano
1

I am an electronics engineer but a newbie to Arduino, so please forgive the stupid questions!
I would like to use a Nano with Serial Input and some other devices connected via SPI, but am a little unsure whether I can do this.
The serial Rx and Tx pins connect to the USB interface, can I connect another serial source to the Rx pin, or will that cause problems?
The SPI Serial Clock appears to be connected to PB5, which is only available on the 6 way pin header, is that correct?
Richard Gunn

2

SCK is on pin 13 as well.

3

If you need usb-serial you can still use softwareserial on some free pin . Not at high baud rates though.

4

Get a different board such as the Mega, it has 4 serial ports, much better then software serial. There are also modules that will give you serial and they connect to the SPI and possibly the I2C bus. This link may help. Arduino RS-232: Serial Communication and Data Interfacing

5

It might be worth looking at the schematic for a Nano if you haven't already.
I don't see any reason why Nano D1/TX couldn't be connected to another device to receive the same input as the serial monitor.
I don't think Nano D0/RX can be connected to another device that wants to send to the Nano. There'd be 2 outputs trying to talk to D0/RX.
I notice the USB chip's reset pin is not connected. Maybe if it was hacked to be in reset mode, it's outputs would go tri-state and then something else could talk to D0/RX

6

There are resistors to protect the multiple devices on the same RX/TX pins. So it's safe to use RX/TX with another device.

Only problem will be that something connected to RX/TX will interfere with uploads over USB.

7

Yes and that would make it safe, in the sense no hardware damage would be done. I suppose the other device could / should be connected to the Nano's RX pin with no resistor or something low like 100R, to avoid a potential divider problem between the USB chip output and the other device's output.
I hadn't considered the above, plus the fact that if nothing is being entered in the serial monitor, then the usb chip won't be sending anything to the Nano's Rx pin.
Thank you for your information.

8

Thanks for all the replies, I think that I will use an Arduino Micro instead of the Nano, as it has a serial port in addition to the USB and the SPI pins are readily available. The Micro is actually the same price as the Nano, so no problem there either.