SN8F2250B datasheet(21/133 Pages) SONIX

21 / 133 page

SN8F2250B Series

USB 2.0 Full-Speed 8-Bit Micro-Controller

SONiX TECHNOLOGY CO., LTD

Page 21

Version 1.1

2.1.1.5 CHECKSUM CALCULATION

The last ROM addresses are reserved area. User should avoid these addresses (last address) when calculate the

Checksum value.

Example: The demo program shows how to calculated Checksum from 00H to the end of user’s code.

MOV

A,#END_USER_CODE$L

B0MOV

END_ADDR1, A

; Save low end address to end_addr1

MOV

A,#END_USER_CODE$M

B0MOV

END_ADDR2, A

; Save middle end address to end_addr2

CLR

; Set Y to 00H

CLR

; Set Z to 00H

@@:

MOVC

B0BSET

; Clear C flag

ADD

DATA1, A

; Add A to Data1

MOV

A, R

ADC

DATA2, A

; Add R to Data2

JMP

END_CHECK

; Check if the YZ address = the end of code

AAA:

INCMS

; Z=Z+1

JMP

; If Z != 00H calculate to next address

JMP

Y_ADD_1

; If Z = 00H increase Y

END_CHECK:

MOV

A, END_ADDR1

CMPRS

A, Z

; Check if Z = low end address

JMP

AAA

; If Not jump to checksum calculate

MOV

A, END_ADDR2

CMPRS

A, Y

; If Yes, check if Y = middle end address

JMP

AAA

; If Not jump to checksum calculate

JMP

CHECKSUM_END

; If Yes checksum calculated is done.

Y_ADD_1:

INCMS

; Increase Y

NOP

JMP

; Jump to checksum calculate

CHECKSUM_END:

…

END_USER_CODE:

; Label of program end

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