This command denotes the start of an assembly program in hexadecimal form. The command must go at the beginning of a program.
Using AsmPrgm is the only built-in way to create assembly programs on the calculator, and it's not very convenient. To use it, after AsmPrgm itself, you must type in the hexadecimal values (using the numbers 0-9, and the letters A-F) of every byte of the assembly program. Even for assembly programmers, this is a complicated process: unless you've memorized the hexadecimal value of every assembly command (which is about as easy as memorizing the hexadecimal value of every TI-Basic token) you have to look every command up in a table.
In addition, it's easy to make a typo while doing this. For this reason, it's recommended not to use AsmPrgm to write assembly programs on the calculator, but instead write assembly programs on the computer. This also lets you use emulators and debuggers and such, as opposed to crashing your calculator (possibly permanently) every time you have a bug.
Just about the only use for AsmPrgm is to enter the hex codes for simple assembly routines that can be called from Basic programs or used for some other short task. For example, the following program will allow you to type in lowercase letters (by pressing ALPHA twice, you go into lowercase letter mode):
To use this, create a program, and enter the code above into it. Then run the program using Asm(. Voila! Lowercase letters are now enabled.
More such short programs can be found here.
TI-84+ Color Calculators
For the TI-84+ C series of calculators, AsmPrgm has been replaced by two new commands: AsmPrgm84C for the TI-84+ CSE and AsmPrgmCE for the TI-84+ CE. The commands function in the exact same manner as the original AsmPrgm command. However, it is important to note that sending assembly programs between a CSE and CE (or vice versa) may cause errors due to a difference in commands.
Many of the hex codes involving AsmPrgm also no longer function correctly on C series calculators. The updated hex codes can be found here.