Bootloader For 18F4520

[isaac]

Hey All
I have being off pic programming for quite a while now due to other commitments
i have only just come back and wanted to continue with my beloved 18F452
and my LAB-X1 Experimenter Board only to find that microchip are recommending the 18f4520 for new designs.
my problem is that i use pbp 2.50 with microcode studio plus but the loader does not contain the bootloader code for the 18f4520 .
i have emailed Mecanique about this since monday but they haven't so far replied to my email.
i have done the online update but its still not there.
I am presently going through the data sheet of the 18f4520 to see what are the things that i need to change in my code the one thing i never used in my program was the caparator all other things are just normal stuff like LCD, A/D
i am i opening up a can of worms with the 18f4520 or is it as easy to use as the 18f452.

Regards
Isaac

[ScaleRobotics]

Isaac,

I have used the PIC18F252 (no zero at the end) bootloader from http://www.etc.ugal.ro/cchiculita/so...bootloader.htm
on a PIC18F2520 chip, and it did work correctly. The site says you can use a PIC18F4520 with the same bootloader code. If you look on the page I linked, you will notice what different chips operate with their Tiny bootloader. This might mean that the same would be true with Micro Code Studio's bootloaders. You might try a couple close chips hex code from MCS, and see if it works.

Or, you could use the Tiny bootloader instead. But I agree, it is nicer to be able to do it right from inside micro code studio.

On a side note, with Tiny Bootloader they give you the assembly code for the bootloader, so you can add in two lines to change the hardware serial port to inverted. That way, you can do without a max232 chip.

As far as the worms, I am not sure if it is a single serving, or family sized can. I have only used the PIC18F2520, and not the predecessors. But if you ever made the move from PIC16 to PIC18 devices, it's got to be a piece of cake in comparison.

Walter

[Ioannis]

Remember that the bootloader cannot protect your code from a reading/copying.

Ioannis

[Charles Linquis]

Ioannis, it is possible for your PBP application code to disable the bootloader by modifying it or erasing it. You can even change configuration registers at run time.


You can get a pretty good level of code protection that way.

I have military customers who want to do a code update, and when they are happy that the load went well, select a menu option. They then get code protection to the limit of what Microchip offers.

[Ioannis]

Hi Charles. Thanks for the post. Can you elaborate on this?

I was pretty sure that Bootloader and Secutity don't go together.

Ioannis

[Charles Linquis]

I don't know about all the others, but the 18F series lets you modify FLASH at run-time. You have to first erase a block, (8-64 bytes, depending on your chip type - and you have to start at a block boundary) with the ERASECODE command. After erasure, you can write whatever you want.
I did this in several versions or "levels". This is the lowest level.

The following to allow the bootloader to run (or not) depending on a program variable. If you set PROTECT and called PatchLoader, the bootloader will not run. If in the program, you set PROTECT = 0, and run it, the bootloader will again work.

It should be noted that this was used with PBP 250a and an 18F8722 and MCLOADER.

PBP2.50a could not access the upper half of the big chips (>64K) memory using READCODE,WRITECODE or ERASECODE, so I had to modify PBPPPIC18.LIB to include a new SYSTEM variable called UPMEM. The library modification set TBLPTRU to UPMEM at the beginning of these 3 routines, and cleared UPMEM at the end (so as not to screw up PBP). By setting UPMEM to 1, I could read the upper half of memory (and by setting it to 0x30, you can set/read the configuration registers). You will see that I need to set upmem before each operation to get to that upper half of FLASH. You wouldn't have to deal with that in a smaller chip.

I have done quite a bit of this, let me know if you need any more help.

PatchLoader:

          UPMEM = 0
      
         ERASECODE $0
       
         WRITECODE $0,$EFE0          ; Change the initial jump vector
         WRITECODE $2,$F0FF          ; 0X1FFC0
 
         WRITECODE $4,$FFFF
         WRITECODE $6,$FFFF
       
         for xx = $8 TO $3E STEP 2    ; Do the rest of the block
         WRITECODE XX,$FFFF
         NEXT Xx
         
         PAUSE 100
         
         PROTECT = 1
         GOSUB PROTECT_UNPROTECT 

         RETURN


PROTECT_UNPROTECT:

         UPMEM = 1     
         ERASECODE $FFC0
        
         UPMEM = 1 
         WRITECODE $FFC0,$6B08
         UPMEM = 1 
         WRITECODE $FFC2,$0000
         UPMEM = 1 
         WRITECODE $FFC4,$0000
         UPMEM = 1 
         WRITECODE $FFC6,$0000
         UPMEM = 1 
         WRITECODE $FFC8,$3F08
         UPMEM = 1 
         WRITECODE $FFCA,$D7FB
         
       if PROTECT = 0 THEN        
             UPMEM = 1 
             WRITECODE $FFCC,$EF82
             UPMEM = 1 
             WRITECODE $FFCE,$F0FE    ; JUMP TO 1FD04
       ELSE  
             UPMEM = 1 
             WRITECODE $FFCC,$EF78
             UPMEM = 1 
             WRITECODE $FFCE,$F0FE    ; JUMP TO 1fcF0
       ENDIF
        
       FOR XX = $FFD0 TO $FFFE STEP 2
             UPMEM = 1 
             WRITECODE XX,$FFFF
       NEXT XX
         
         RETURN

REPROTECT:
         UPMEM = 1
         READCODE $FFCC,X
           IF X = $82 THEN
            HSEROUT [13,10,10,"Reprotecting Loader",13,10]
            PROTECT = 1
            GOSUB PROTECT_UNPROTECT
           ENDIF 
          RETURN  
          
GetTypeLoader:
         READCODE 0,TypeLoader
         RETURN