The 80 hex is sent as a synchronization character before each
transmission. The device responds with a 90 hex as an acknowledge.
Then a data frame is sent. Each frame begins with a header byte =
80 hex. The other bytes of the frame follow the 80 hex header
immediately. The correct format of the BSL data frames are defined
in the application note `Features of the MSP430 Bootstrap Loader`
SLAA089 available in the MSP430 website.
A careful examination of the code included with the application
note `Application of Bootstrap Loader in MSP430 w/Flash - Hardware
and Software Proposal` SLAA096 shows that this is the proper
technique. The software and hardware in that application note have
been tested and proven to work.