After fooling around all day trying to figure out why WRITECODE sometimes works properly and sometimes doesn't (see my other WRITECODE thread), I think I'm finally getting somewhere.

Using Jumper's suggestion for using DEFINE RESET_ORG 'X', I built a tiny program that loads into memory location 64 (40h). I then copied the object code from the hex file that resulted from compiling this little program and I inserted it into DATA statements in my loader program.

Also per Jumper's idea, I modified the LOADER_USED define in the .lib file so that it located the loader program high up in memory - at 60160 to be precise. My loader program reads the program bytes out of the EEPROM where DATA put them, and WRITECODEs them into their intended executable Flash memory locatinos starting at 64 (40h). It then uses an "@ GOTO 64" to jump to the "downloaded" program.

Eureka - It works!

So now the basic mechanisms are working. What has to be done next is to work out a data transfer protocol and write a small VB application to send the .hex file contents to the PIC. This won't be trivial I think, because each line of the hex file has to be parsed and a 'padding' scheme will have to be developed because not all lines of the .hex file are equal in length.

Thanks for the help Jumper. My available time to work on this will decline after this week but I fully intend to pursue it until it's complete

Joe