# Serial Link Between 3.3V devices

I have an RPi and a freescale FRDM-KL25z controller which will talk over serial protocol. I'm using the pyserial library on the pi:

import serial
ser = serial.Serial('/dev/ttyAMA0', 9600)
ser.write('hi FRDM')


and using the serial protocol from the mbed library will generate interrupts to process the data from the Pi.

https://developer.mbed.org/users/mbed_official/code/mbed/docs/4fc01daae5a5/classmbed_1_1SerialBase.html#ae67fb9b5a2ee2f4e98a39cdab10ed090

My question is, having two devices which talk over the same protocol at the same potential and in close proximity, do I need a logic level converter or some form of UART chip?

I would think not, but I am aware that RS232 is a +-12V protocol so would just like to ensure that this assumption is correct.

• If you're using /dev/ttyACM0 then you're using CDC/ACM not RS232. – Majenko Jan 1 '15 at 16:51
• does that mean this code uses one of the USB ports? I plan to use the GPIO pins 8 and 10. – Mark Corrigan Jan 1 '15 at 16:53
• Yes, that code is using USB. For the hardware UART you would use /dev/ttyAMA0 instead. – Majenko Jan 1 '15 at 16:58