Externally powering target board

The AVss-Pin is connected to ground, so it has no positive voltage to power anything. Generally your supply pins are all input, and if you connect one of them to an external device it will be connected in parallel to your microcontroller, so it should be okay to connect another device to the supply rails VCC430 and GND (in the schematics). Just make sure your device doesn't draw to much current.

If you want to switch the device on and off with your MSP, you can connect the supply of it to one pin and the ground to GND, but be sure your device draws less current than the MSP can source (a few milliamps).

Your external device should also have some bypass capacitor (100nF) near the supply pins of it to reduce noise.

As for external supply, you generally want to have a low noise supply for best results (especially in analog/mixed signal designs). So don't use a switch mode supply directly but a linear regulator, if you want to connect a bench supply, it should be okay as they are most of the time linear regulated. Also for experiments it's good to set some current limiting in your supply so if something goes wrong not everything will be fried.

Hi,

Ya sorry I meant the AVcc and AVss to power another device. The device in question is a level shifter for UART to RS232 communication (consumes no more than 8mA) so I don't think that should be a problem?

Oddly enough, pin 13 of the MSP430AFE253 (ground) is not connected to the header. No big deal though, because AVss connects to ground so I can just use that one. 

Thank you for the support,

-Larry

Hi Larry,

8 mA should be no problem, normally the debuggers can source up to around 100 mA. And yes connecting to AVcc and AVss should pose no problems.

What I find rather strange though is that you are saying the pin 13 has no connection to the header. In the layout all of the GND pins on the board are connected together with a big ground plane. Maybe there is something wrong with that board?