To single step through the simulation click the Single Step Simulation button on the toolbar, select the SimulationàStep menu option or press the F7 shortcut key. This will step the simulation forward by one step.
With the Source Code and the Special Function Registers windows open you will see the source line increment to indicate that during the last step that line of source was executed. Any changes to Special Function Registers will be shown in the Special Function Registers window in RED to highlight the change. Sometimes when you click the step button nothing seems to happen but when you step a second time the source code steps again. This is because some PIC instructions require two steps to complete the instruction and the simulation executes in one step increments.
Repeatedly pressing the single step button will show the source code for this example going around a very simple loop that grabs the value from the TIMER0 register and then pushes it onto the PORTB output. Every ten steps, which is the period of the TIMER, the RTCC will receive the rising clock edge it requires to trigger the increment of TIMER0 which occurs independently of the main loop. All of this happens before your very eyes in single step mode which allows you view and compare expected values. Single stepping is a seriously useful tool; the other seriously useful tool you will use often in conjunction with single stepping is the breakpoint.
A breakpoint is a line of source code at which a running simulation will automatically be halted. You can then single step from that point onwards. This allows you to set breakpoints in remote sections of the code and run the simulation up to that point before single stepping. Virtual Breadboard allows any component to support breakpoints. The PIC Debugger supports breakpoints using the source code window.