WRITECODE - How it works

[pedja089]

As far as I understand how it work, it won't save nothing to FLASH until page you write to last byte in table. So random write to code using WRITECODE might not be good idea.

ASM for WRITECODE Adr, FlashByte1 'Adr VAR LONG

               Line           Address        Opcode         Label          DisAssy    
               63459          1EFC4          C02E           Z0007E         MOVFF Adr, TBLPTR
               63460          1EFC6          FFF6                          NOP            
               63461          1EFC8          C02F                          MOVFF 0x2F, TBLPTRH
               63462          1EFCA          FFF7                          NOP            
               63463          1EFCC          C030                          MOVFF 0x30, TBLPTRU
               63464          1EFCE          FFF8                          NOP            
               63465          1EFD0          502A                          MOVF _FlashByte1, W, ACCESS
               63466          1EFD2          DEA9                          RCALL 0xED26

First address is loaded to pointer registers(4 bytes), then your byte is loaded to work registers, and then WRITECODE is called with RCALL.
Here is code for WRITECODE macro for 128 byte page

               Line           Address        Opcode         Label          DisAssy    
               63124          1ED26          6EF5           WRITECODE      MOVWF TABLAT, ACCESS
               63125          1ED28          000C                          TBLWT*         
               63126          1ED2A          28F6                          INCF TBLPTR, W, ACCESS
               63127          1ED2C          0B7F                          ANDLW 0x7F     
               63128          1ED2E          E109                          BNZ 0xED42     
               63129          1ED30          0E84                          MOVLW 0x84     
               63130          1ED32          6E7F                          MOVWF EECON1, ACCESS
               63131          1ED34          0E55                          MOVLW 0x55     
               63132          1ED36          6E7E                          MOVWF EECON2, ACCESS
               63133          1ED38          0EAA                          MOVLW 0xAA     
               63134          1ED3A          6E7E                          MOVWF EECON2, ACCESS
               63135          1ED3C          827F                          BSF EECON1, 1, ACCESS
               63136          1ED3E          0000                          NOP            
               63137          1ED40          947F                          BCF EECON1, 2, ACCESS
               63138          1ED42          EFE8           writecodedone  GOTO 0x1EDD0   
               63139          1ED44          F0F6                          NOP   
....
               63209          1EDD0          0100           DUNN           MOVLB 0x0      
               63210          1EDD2          0000           DUNN5          NOP            
               63211          1EDD4          0012                          RETURN 0

Then at WRITECODE byte from w is moved to holding register, and then table write is executed(TBLWT*).
This will check if your last adr is 127

               63126          1ED2A          28F6                          INCF TBLPTR, W, ACCESS
               63127          1ED2C          0B7F                          ANDLW 0x7F     
               63128          1ED2E          E109                          BNZ 0xED42

If not it will branch to writecodedone, then goto to DUNN and finally RETURN to your code.
If last Adress was 127 then it will execute FLASH write(Same as EEPROM write, just bit EEPGD of EECON1 is set ) and go back to your code.
If you put address 127 and load only one byte page write will be executed, but what is in table you can't know, so table will be write with random data except byte at 127 location.
I hope that this will help you to understand how WRITECODE is done.
This might be separate topic, as it doesn't have much with new version.