Bootloader with 16F877

[wwoodrow]

Hello, we have a set of old code that we want to give the ability of a bootloader. We want to be able to set a flag in memory that the bootloader can read. But not sure where to write to or whether there is a better way. We have our main program running; we issue a serial command of 'z' and will cause the program to write to memory that can be read from the bootloader. Then the main program will issue a reset and upon startup the bootloader will read that memory and know if it needs to wait for a new code upload. We can't use a variable since the variable will be cleared upon a reset. We have no way to use a button or a physical way of telling it to load like in the example program that came with the complier.

Any help would be appreciated.