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Normally, ATMbL’s AVR microcontrollers are progrDmmed XVLng prRgrDmmers. There are many ways to program Whe AVR mLFrRFRnWrROOerV, VXFh DV in-system programming, parallel progrDmmLng Dnd XVLng ERRWORDder. Advantage with the bootloader method LV WhDW yRX dRn’W need Dny exWernDO hDrdwDre WR ORDd Whe hex fiOe Rn Whe microcontroller. A bootloader program is placed inside the boot section of the )ODVh memRry, WR hDndOe FRmmXnLFDWLRn wLWh Whe hRVW PC Dnd IDFLOLWDWe prRgrDmmLng RI ERWh )ODVh Dnd ((PROM.

Programming using bootloader

7he ERRWORDder firmwDre ORDded Rn Whe microcontroller allows in-system programming directly via TuD and RuD pins of the microcontroller. The code responsible for in-system programming via serial port resides in the configXrDEOe ERRW memRry VeFWLRn RI Whe mLFrRFRnWrROOer. :hen VLgnDOOed XVLng external switch while resetting the microcontroller, it gets active and waits IRr FRmmXnLFDWLRn IrRm Whe PC IRr ORDdLng Whe hex fiOe Rn Whe mLFrRFRnWrROOer’V flDVh memRry. 7he PC VendV 1 1 0 0 Whe hex fiOe WR Whe mLFrRFRnWrROOer. 7he code residing in the boot section loads Whe hex fiOe Rn Whe mLFrRFRnWrROOer’V flDVh memRry.

lnce the programming process is complete, newly loaded code can be exeFXWed Ey preVVLng reVeW. OnFe Whe code is loaded on the microcontroller, UAR7 LV Iree Dnd FDn Ee XVed IRr RWher applications.

Note that the bootloader gets invoked only if boot switch is kept pressed while the microcontroller is reVeW XVLng reVeW switch.

The Flash memo-

Fig. 2: Circuit to program the microcontroller using the bootloader

Fig. 1: Program memory organisation