PIC Bootloader

Using bootloader is the most convenient way for PIC programming, especially when you are debugging your program and need to transfer it to the target PIC chip many times in short time. The hardware request is that there is a serial communication interface implemented between the target PIC board and the PC. The bootloader solution presented here is intended to be used with 16F877(A) microcontroller. As all other bootloaders, this solution consists of a Windows application running on the PC and bootloader firmware running on the target PIC chip.

Windows application for downloading HEX files to the target PIC chip running the bootloader can be downloaded here.

The bootloader firmware is given in the form of Basic source program that has to be compiled with PIC Simulator IDE integrated Basic compiler to get the HEX file ready to be programmed into the microcontroller. The correct microcontroller model needs to be selected - 16F877(A), and the selected clock frequency is supposed to be at least 8MHz.

PIC bootloader firmware:

#define CONF_WORD = 0x3f72
StartFromZero

Dim i As Byte
Dim j As Byte
Dim total As Word
Dim eraseblock As Byte
Dim programblock As Byte
Dim address As Word
Dim data(4) As Word
Dim dat As Word
Dim din As Byte
Dim counter As Word

ASM:        BSF PCLATH,3
ASM:        BSF PCLATH,4
Goto bootloader_start

'beginning of user program
ASM:        ORG 0x0004
user_program:
Goto user_program

'beginning of bootloader
ASM:        ORG 0x1C00
execute_user_program:
ASM:        BCF PCLATH,3
ASM:        BCF PCLATH,4
ASM:        GOTO 0x0004
ASM:        NOP

ASM:        ORG 0x1D00
bootloader_start:
UART_Init 19200
WaitMs 100
UART_Write 0x55
For i = 1 To 100
	WaitMs 1
	UART_Get j
	If j = 0x55 Then
		Goto bootloader_main
	Endif
Next i
Gosub reset_state
Goto execute_user_program

bootloader_main:
Gosub get_byte
total.LB = din
Gosub get_byte
total.HB = din
'total is the last address to be programmed
Gosub get_byte
eraseblock = din
Gosub get_byte
programblock = din
address = 0x0000
For counter = 0 To total Step programblock
	j = programblock - 1
	Gosub get_data
	For i = 0 To j
		Gosub prepare_write
		Gosub write_flash_memory
		address = address + 1
	Next i
Next counter
address = 0x1c00
j = 3
Gosub get_data
For i = 0 To j
	Gosub prepare_write
	Gosub write_flash_memory
	address = address + 1
Next i
WaitMs 100
Gosub reset_state
Goto execute_user_program
End

get_data:
For i = 0 To j
	Gosub get_word
	data(i) = dat
Next i
Return

get_word:
Gosub get_byte
dat.LB = din
Gosub get_byte
dat.HB = din
Return

get_byte:
UART_Read din
UART_Write din
Return

prepare_write:
EEADR = address.LB
EEADRH = address.HB
dat = data(i)
EEDATA = dat.LB
EEDATH = dat.HB
Return

write_flash_memory:
ASM:        BSF STATUS,RP0
ASM:        BSF STATUS,RP1
ASM:        BSF EECON1,EEPGD
ASM:        BSF EECON1,WREN
ASM:        MOVLW 0x55
ASM:        MOVWF EECON2
ASM:        MOVLW 0xAA
ASM:        MOVWF EECON2
ASM:        BSF EECON1,WR
ASM:        NOP
ASM:        NOP
ASM:        BCF EECON1,WREN
ASM:        BCF STATUS,RP0
ASM:        BCF STATUS,RP1
Return

reset_state:
RCSTA = 0
TXSTA = 0
EECON1 = 0
PIR1 = 0
PIR2 = 0
STATUS = 0
Return

20th Anniversary of theOSHONSOFT PROJECT(2001 - 2021)

PIC Bootloader

20th Anniversary of the
OSHONSOFT PROJECT
(2001 - 2021)