Rev. A - 12-Jan-01 3
ANM095
2.3.Hardware Bit BLJB
The Boot Loader Jump Bit (BLJB) is a bit of the hardware byte. Its value can be modified in parallel programming
mode only. The values and uses are:
-0: After reset, the bootlader is executed at FC03h. This mode is the most versatile and gets full benefits
of the Flash thanks to the Flash Bootloader.
-1: After reset, the application program is executed at 0000h. The application program is loaded in parallel
mode. This mode is used when the customer application program is stable. Parallel mode is re-used to
change the program loaded in Flash.
2.4.Bootloader Flash Program
The default bootloader Flash is located in address space from FC00h to FFFFh. As it is in a Flash memory, its
value can be changed.
The boot loader lock bit (BLLB) is an hardware bit which locks the content of the bootloader Flash program. This
prevents any programming access to the upper 1-KByte in parallel mode only.
If erased, the Flash bootloader can be restored by parallel programming. The default Atmel bootloader program is
available on our website.
The Bootloader Flash program can be executed in two ways:
•Hardware conditions EA=1, PSEN=0, ALE=1 or no connected. In this case the PC is forced to value FC00h.
This permits a boot from the default bootloader in all configurations and thus a return to the original device
configuration.
•Hardware and software method. The boot loader jump bit (BLJB) is an another bit of the hardware byte.
Its value can be modified in parallel programming mode only. The values and uses are:
-0: After reset, the bootlader is executed at address FC03h. This mode is the most versatile and gets full
benefits of the Flash thanks to the Flash Bootloader. Depending on the status of the device, the process
will be different. The boot modes are detailed in paragraph 4.
-1: After reset, the application program is executed at address 0000h. The application program has been
loaded in parallel mode. This mode is used when the customer application program is stable. He will
need to reuse the parallel mode to change this configuration.