AT89C51ID2-SMSIM ATMEL [ATMEL Corporation], AT89C51ID2-SMSIM Datasheet - Page 124

• Manufacturer Part Number: AT89C51ID2-SMSIM
• Description: 8-bit Flash Microcontroller
• Manufacturer: ATMEL [ATMEL Corporation]

Bootloader Functionality
Introduction
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AT89C51ID2
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 a an output port in normal operating mode after reset, user application
should take care to release PSEN after falling edge of reset signal. The hardware condi-
tions 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 Figure 49
Hardware Conditions
BLJB
SBV
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.
Purpose
4289A–8051–09/03