AT89C51RB2-RLTCM ATMEL [ATMEL Corporation], AT89C51RB2-RLTCM Datasheet - Page 91

• Manufacturer Part Number: AT89C51RB2-RLTCM
• Description: 8-bit Microcontroller with 16K/ 32K Bytes Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Bootloader Functionality
Introduction
4180B–8051–04/03
The bootloader can be activated by two means: Hardware conditions or regular boot
process.
The Hardware conditions (EA = 1, PSEN = 0) during the Reset# falling edge force the
on-chip bootloader execution. This allows an application to be built that will normally
execute the end user’s code but can be manually forced into default ISP operation.
As PSEN is an output port in normal operating mode (running user application or boor-
loader code) after reset, it is recommended to release PSEN after falling edge of reset
signal. The hardware conditions are sampled at reset signal falling edge, thus they can
be released at any time when reset input is low.
The on-chip bootloader boot process is shown in Figure 37.
Hardware Conditions
BLJB
SBV
Purpose
The Hardware Conditions force the bootloader execution whatever BLJB, BSB
and SBV values.
The Boot Loader Jump Bit forces the application execution.
BLJB = 0 => Boot loader execution.
BLJB = 1 => Application execution.
The BLJB is a fuse bit in the Hardware Byte.
That can be modified by hardware (programmer) or by software (API).
Note:
The BLJB test is perform by hardware to prevent any program execution.
The Software Boot Vector contains the high address of custumer bootloader
stored in the application.
SBV = FCh (default value) if no custumer bootloader in user Flash.
Note:
The costumer bootloader is called by JMP [SBV]00h instruction.
AT89C51RB2/RC2
91