The F3 function switches the display between Source mode, Mixed mode, and Assembly mode. You can also switch display modes by choosing the Source Window command from the Options menu and then selecting a display mode in the Source Window Options dialog box. (If the source-code text file cannot be located, CodeView automatically disassembles the executable file and displays it in assembly-language form.)
The Source mode shows the program as you wrote it. The Mixed mode and Assembly mode each expand macros and code-generating directives (such as .STARTUP) into assembly-language instructions. You can execute these instructions one at a time (rather than as a single item), and verify that the assembler has created the correct instructions from the macro or the directive.
Figures 15.5 and 15.6 show Mixed mode and Assembly mode, respectively, for the same code.