There is no code dependancy, no. The MSP talks to the emulation side of the LaunchPad which is powered by the PC's USB. The system runs at ~3.3V generated by a LDO that is powered from the 5V. GND, TX and RX must remain connected for the communication, but instead of having the MSP powered from the LDO's 3.3V as well, you now want to cut this connection and power the MSP from somewhere else. Since the emulation side still sends data to the MSP at it's supply levels of 3.3V you have to power the MSP externally with this voltage as well. Otherwise when having a too large difference, the protection diodes of the MSP might turn on at it's RX line which can cause damage. I don't know if there are series resistors in the communication lines that would limit this current. If so, things could be different. Check the hardware design files for this information. On the other hand, if the voltage of the MSP is too low, the emulation side might not recognize the high level of the MSP properly.
↧