Hi Annibal,

to have a bootloader I went another way: I use an external RAM (32k) and a 256k Flash, where in Page 0 (64k space) the bootloader resides. To update the Bootloader (max size = 32k), I load the new code to Ram, switch then the PSEN <-> RD / WR so that the RAM becomes code, then copy the RAM back to Page 0.

To update page 1..3 with Application Code, I switch to Bank 0, copy the bootloader to RAM, and again switch to execute in RAM PSEN <-> RD / WR and now can update the desired code to Bank 1..3.

Thus I will not need jumps in bootcode, I can use external RAM in normal programs, and with some derivats where there is XRAM available (C515C/C390 etc) I can still use this also in the bootloader running in RAM.

Another advantage is, that besides of a Switch Function at a defined Adress Location for both the bootloader / application programs, I can use completetly independent code / source for both.

The PSEN <-> RD/WR switching is done with a 74HC(AC)157

Werner