Open the project Breakpoints.X

If you haven't already done so, click on the Open Project button and open the Breakpoints.X project. If you have not downloaded the Breakpoints Project yet, you can find it in the Exercise Files section of this page.

Set a Data Breakpoint

If the breakpoint tab isn’t already open, select from the menu:
Window > Debugging > Breakpoints.

In the window’s sidebar, click on the Create new breakpoint button:

Configure Data Breakpoint

In the window that opens:

• Set Breakpoint Type to Data
• For the Symbol, click on the Symbols button
• Select the SFR's radio button, and select PMDIN1 from the list, then click the OK button.

The Address field should automatically populate after performing the step above.

• For Breaks on, select Write Specific Word.
• For the Value, enter 0x003C (the ASCII value for ‘<‘ = 0x3C = 6010)
• For the Pass Count Condition, leave it set to Always Break.
• Click OK.

Debug the Project

Click on the Debug Project button:

Open the Disassembly window

Open the Disassembly window. You should see something like the following:

If you look two instructions above the program counter’s position (green arrow in glyph margin, green highlight in editor) you will see a line that writes to the PMDIN1 register. So it looks like we caught our event. However, if you scroll to the top of the Disassembly window you will see that the first line is, !void lcdInit(void).

So we are in the LCD initialization routine, not lcdPutChar(), which writes text to the display. Look at the Watches tab that you should have opened at the very beginning of the lab:

The value in PMDIN1 is indeed the value we were looking for. The problem is that this is a command to the LCD module that happens to have the same data that we were looking for. This value is not a character being written to the display, so it isn’t what we want.

Continue to run the program

Since we are still in the lcdInit() routine, we haven’t even begun to write text to the display. We need to continue the program to get to the point we are interested in.

Click on the Continue button:

The program should run again until the next breakpoint event.

Observe the second event

When the program halts a second time, the Disassembly window should automatically pop up. You should see something like the following:

Now we can clearly see from the top line that we are in the lcdPutChar function, which means that data is being written to the LCD instead of initialization commands. This is more promising. Look at the Watches tab again to verify that PMDIN1 contains the data we are looking for:

This is much better. This is what we were looking for. Notice also that there was skid involved, just like with address and line breakpoints. The Program Counter is two instructions past the event where the program wrote to PMDIN1. As a result, there was enough time for the character to be displayed on the LCD before the program stopped. The LCD should be showing:

Also, you may have noticed the gray highlight and gray box in the glyph margin on line 10, where the write to PMDIN1 takes place. This is the disabled address breakpoint we set in the previous exercise. It had no effect at this time.

Clean up for the next exercise

Do not remove or disable the data breakpoint at this time. We will be using it in the next exercise on Tuples.