Trying to communicate with an external board through Arduino
I think it's best not to over engineer anything here. Just use a voltage divider. Arduino uses 5V, MSP uses 3.3V. So... 5V*20k/(10k+20k) = 3.3V. However, MSP is powered at 3.3V...so use something like 5V*10k/(10k+10k) = 2.5V. What this means is that you need to connect the Arduino's Tx line to voltage divider to MSP's Rx line. From MSP's Tx line to Arduino's Rx line, no need for voltage divider because it's only 3.3V. Done.