Hello!
I think you are talking about SPI bi-wire (SBW), which can be used instead of the regular JTAG.
There are probably many arcitles about SBW on TI's site.
Now, just to be sure about what you are doing: you mean that you are using launchpad as a
programming device, right? (You removed its processor or at least the jumpers, and use it to
program your board?). Basically if you just want to program your board, you don't have to care too
much about how it happens, it just works. If you are building a custom programmer, that's another
story.
Dora.