FLASH_API:
         PUSH    IE          ;DISABLE INTERRUPTS
         CLR     EA
         XCH     A,R1
         PUSH    ACC
         MOV     A,R1
         MOV     R1,R0B0     ;SETUP OPERATION CODE
         ANL     FCF,#0FCh   ;enable boot sector - !!! this command MUST be located ABOVE 2000h!!!
         CALL    01FF0H      ;call to ISP_API (modifies B register but no Rx)
         ORL     FCF,#001h   ;switch back to user FLASH
         MOV     R1,A
         POP     ACC
         XCH     A,R1
         POP     IE
         RET