EMBEDDED BOOTLOADER

INTRODUCTION:

1. It is a technique of burning the code into the microcontroller in the absence of an external programmer.

REQUIREMENTS:

1. Entight connection from board to pc via USB.
2. One microcontroller(PIC) already programmed with a bootloader.

INSTALLATION STEPS:

STEP 1:

• For the bootloader to operate properly we need to access  boot mode.

• Don’t let go the reset button until the activation of boot mode when the USB cable is attached to the port.

STEP 2

• Note that the required driver installation will fail due to the absence of the drivers by default, therefore we have to install them manually.

STEP 3:

• UPDATE  UNKNOWN DEVICE DRIVERS

STEP 4:

• From the given popup window select browse for drivers

STEP 5:

Enter the path to where the corresponding drivers can be found in directory path and after that click install.

STEP 6:

STEP 7:

• Now we can view the microchip device from the device manager settings under all settings tab.

VECTOR MAPPING:

• Writing code for a bootloader is quite analogous to what we used to perform  in cases except for some slight variations.
• The main difference comes where the user program starts from the address 0x800.
• Therefore  the address of the reset vector should be at 0x800.
• Normally , reset is in position 0x00 and the interrupt vectors are in 0x08 and 0x18, therefore they have to be remapped.

PROCEDURE:

• You have  to set the code offset as 0x800 for the project to be compiled.
• For that that,  project properties ->xc8 linker.
• Then from the Options Categories  menu, click on  Additional options.
• Finally add  800 corresponding to the displayed  code offset box.

BURNING NEW PROGRAMS USING BOOTLOADER:

• Initially Boot into bootloader mode by pressing the reset key without leaving it   via connecting the USB cable until boot menu shows up.
• Next click on the PDFUSB.exe file  from the Pdfusb folder.
• Afterwards select PICUSB 0 as the boot  device.
• Finally dump the hex file via button.
• Suppose the loaded code starts from a random memory than 0x800,  you will need to put an extra line to your created hex file.
• Observe that the text circled in red  is 4262E20, which points to the starting address.

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