EF2851 is a call to an operating system routine, 0x5128 (notice the numbers are swapped). It is called _ResetDefaults and you can find other such "bcalls" here (just do ctrl+f and search for 5128)
C9 translates to assembly as an RET instruction which translates to English as "return." In assembly, code structures are all about routines and subroutines. The main routine might call a sub routine, and once that sub routine ends (usually signified by an RET), it returns to the main routine where it left off. Your assembly program is compiled, allotted RAM, and then run as just another sub routine, basically :P
On the TI calcs, EF signifies that the next to bytes are actually an ID/address for a much more complicated routine built into the TI operating systems.