In BOOTSTRAP MODE only the internal memory portions of the 64K address space are used. The small on-chip ROM at address $BF40-$BFFF is enabled when the 68HC11 is reset in the special bootstrap mode. The reset vector ($BF40) at address $BFFE and $BFFF is loaded in the program counter and the 68HC11 proceeds to execute the firmware at this location. The 68HC11 initializes the on-chip SCI with 1200 Baud (Quarz 8 MHz) and sends a break ($00). The reset sequence in BOOTSTRAP MODE 
The user then sends from PC a $FF character and now the 68HC11 is ready to accept 256 bytes of program data, which will be put into on-chip RAM beginning at address $0000. These characters are echoed out. When the 68HC11 receives the 256th byte, a jump is executed to RAM location $0000, and the loaded user program gains control. With this user program in the internal RAM of 68HC11 we can save bytes in the eeprom and they are the final program. The last instruction in the user program is a jump to the first eeprom location (eg. JMP $B600). Direct program start in the internal eeprom after reset. Connect RX and TX on RS232 together. The break signal transmitted from 68HC11 is now echoed. The bootloader firmware executes a jump to the internal eeprom and if we have downloaded before program datas in this memory location, this program gains control. |