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8 Channel LED Chaser
for 16F628A
  • Quick guide to assembling firmware with MPLAB

This is a very quick guide to allow you to edit the sequence data and then reassemble the code to get the HEX file needed to program into the PIC microcontroller.  It's not a comprehensive guide to using the MPLAB IDE and it's not intended to be...

  • Download the LED Chaser source code and unzip all the files to a working directory.
    Tip: the MPASM assembler doesn't like directory path + file name to be  longer than 62 characters so avoid unzipping into a directory in 'My Documents', instead create one off the root of C:, for example c:\pic\chaser\
     
  • Run the Microchip MPLAB IDE application and open the .asm file and the sequence data file.  These are highlighted in the screen shot below.  File names may vary slightly with different firmware versions.
     
  • The files with a .inc extension are include files. They are named in the .asm file and are read by the assembler during the Quickbuild, don't change or delete them.

  • From the Configure menu open 'Select Device'

  • Select the PIC from the drop down list as shown below.
     
  • You will find both 16F628 and 16F628A in the list, select the correct type that you will be using.

  • You can create, edit and change the sequences in the sequence data file.  When you've done, save the file before going to the next step.  Guide to sequence data format

  • Highlight the pwmc_mainxxx.asm editing window.
     
  • Next select Quickbuild from the Project menu.  The Quickbuild option will run the Microchip MPASM assembler that creates the .HEX file from the source .asm and .inc files. 
     
  • Note: if the Quickbuild menu option doesn't show the name of the .asm file, you haven't selected the window in the last step.

  • Once the Quickbuild has finished check the output window to make sure the build succeeded.   If you get the 'Build Succeeded' text at the end you will find a .HEX file in the working directory with the same name as the .asm file.  e.g.  pwmc_main123.asm will generate a file named pwmc_main123.HEX if the build is successful.
     
  • If there are any errors reported here, or the build fails you need to investigate and fix them before programming the PIC.  Be aware that if the .HEX file already exists from a previous successful build and the build subsequently fails, the .HEX file in the working directory is the one from the last successful build.  (this is a tip worth remembering before wasting hours trying to understand why the changes you make don't appear to work:-)

  • After a successful build, if you look in the working directory you will see a file with a .lst extension.  If you open this file in a text editor and go to the very end of it you will see a memory usage map.  This is a quick way to see how much memory has been used and how much there is left to add extra sequences into.

MEMORY USAGE MAP ('X' = Used, '-' = Unused)


0000 : X---XXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0040 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0080 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
00C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0100 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0140 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0180 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
01C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0200 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0240 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0280 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
02C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0300 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0340 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0380 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
03C0 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0400 : XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXX
0440 : XXXXXXXXXXXXXXX- ---------------- ---------------- ----------------
2000 : -------X-------- ---------------- ---------------- ----------------

All other memory blocks unused.

Program Memory Words Used: 1100
Program Memory Words Free: 948


Errors : 0
Warnings : 0 reported, 0 suppressed
Messages : 0 reported, 3 suppressed

  • The sequence data file that will be used when the firmware is assembled is named in the pwmc_mainxxx.asm file.
     
  • You can have a number of different sequence data files and specify the one you want to use in the .asm file before assembling.
     
  • In the example screen shot below there are three different sequence data files.  One is used and the other two are commented out. When the code is assembled it will use the pwmc_SeqData.inc file.
    (In MPLAB any text on the line after the ';' semicolon is treated as a comment)