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Segment A of the information memory is locked separately from all other segments with the LOCKA bit. If LOCKA = 1, segment A cannot be written or erased, and all information memory is protected from being segment erased. If LOCKA = 0, segment A can be erased and written like any other flash memory segment.
The state of the LOCKA bit is toggled when a 1 is written to it. Writing a 0 to LOCKA has no effect. This allows existing flash programming routines to be used unchanged.
; Unlock Info Memory
MOV #FWPW,&FCTL4 ; Clear LOCKINFO, if set
; Unlock SegmentA
BIT #LOCKA,&FCTL3 ; Test LOCKA
JZ SEGA_UNLOCKED ; Already unlocked?
MOV #FWPW+LOCKA,&FCTL3 ; No, unlock SegmentA
SEGA_UNLOCKED ; Yes, continue
; SegmentA is unlocked
; Lock SegmentA
BIT #LOCKA,&FCTL3 ; Test LOCKA
JNZ SEGA_LOCKED ; Already locked?
MOV #FWPW+LOCKA,&FCTL3 ; No, lock SegmentA
SEGA_LOCKED ; Yes, continue
; SegmentA is locked
; Lock Info Memory
MOV #FWPW+LOCKINFO,&FCTL4 ; Set LOCKINFO
