The above, as stated, is not true^[1]: the Keil Debugger does run the code in the actual 8052.

However, I am now fairly certain that you must be talking about the Keil simulator - not the debugger.
In this case, it is true that you are not running on an actual 8052 in your actual target hardware - you a running a simulation using the PC.


You must understand the limitations of simulation - as I explained before:




[1] Actually, all testing & measurement involves some disturbance of the system under test:

When you take a voltage reading, you load the circuit - which affects the voltage;

When you take a current reading, you add extra series resistance - which affects the current

etc, etc,...
See Heisenberg's Uncertainty Principle.

Similarly, any form of debugging has some impact on the software under tes:

Using LEDs, you have to add code to drive the LEDs;

Adding debug trace with printf uses memory space & processor time;

A monitor uses processor resources;

Even an ICE can add loading on the processor pins, and introduce all sorts of problems with actually connecting it to the target system

Thus there is no such thing as entirely non-intrusive debugging - no matter what tools you have.