Changes

The first file ("DAC_box") has a funny little icon next to it: three rectangles, the topmost of which is green.  That icon means that the DAC_box file is the "top module".  You can synthesize the top module, but the others cannot be synthesized.  Since you'll want to synthesize different components at different times, just remember that before synthesis you have to reset your top module.  This is done by right clicking on the file you want set as top and selecting '''Set as Top Module.'''

The first file ("DAC_box") has a funny little icon next to it: three rectangles, the topmost of which is green.  That icon means that the DAC_box file is the "top module".  You can synthesize the top module, but the others cannot be synthesized.  Since you'll want to synthesize different components at different times, just remember that before synthesis you have to reset your top module.  This is done by right clicking on the file you want set as top and selecting '''Set as Top Module.'''

You can see that ISE has established a hierarchy of files.  The DAC_box has a DAC_controller and a DAC_emulator.  The DAC_controller has a DAC_hold19, a DAC_shiftreg, and a DAC_delay, and the DAC_emulator part list is collapsed.  In front of each of these files lower in the hierarchy there is a u number.  The u number is a shorthand designation of which part is which (discussed in [[VHDL:_The_real_code#Putting_it_together:_components]]).  Your files can appear in multiple places, as well.  For example, the DAC_subemulator (no u number because it is an independent part not used in the DAC_box) has a DAC_hold19 and a DAC_shifter.

You can see that ISE has established a hierarchy of files.  The DAC_box has a DAC_controller and a DAC_emulator.  The DAC_controller has a DAC_hold19, a DAC_shiftreg, and a DAC_delay, and the DAC_emulator part list is collapsed.  In front of each of these files lower in the hierarchy there is a u number.  The u number is a shorthand designation of which part is which (discussed in [[VHDL:_The_real_code#Putting_it_together:_components|VHDL:_The_real_code]]).  Your files can appear in multiple places, as well.  For example, the DAC_subemulator (no u number because it is an independent part not used in the DAC_box) has a DAC_hold19 and a DAC_shifter.