Texas Instruments MSP430x1xx - Manual (Page 435)

Flash Memory Access via JTAG and Software
C-23
Flash Memory
C.5.3.1 Example: Programming One Word Into a Flash Memory Module via Software
Execution Outside this Module
This example assumes that the code to program the flash location is not
executed from the target flash memory module.
BUSY = 1
yes
yes
no
no
BUSY = 1
Lock = 1
Lock = 0, WRT = 1
Write Data to Flash Address
Disable all Interrupt Sources
and Watchdog
Restore or Enable Required
Interrupt Sources and Watchdog
Fxkey .set 03300h
Fwkey .set 0A500h
; No interrupt request may happen while the flash is programmed
Test_Busy1
BIT #BUSY,&FCTL3
JNZ Test_Busy1
MOV #Fwkey,&FCTL3 : Clear lock bit
MOV #(Fwkey+WRT),&FCTL1: : Enable write to flash
MOV #123h,&0FF1Eh : Write a word to flash
Test_Busy2
BIT #BUSY,&FCTL3 ; still busy?
JNZ Test_Busy2 ; yes, repeat busy test
MOV #Fwkey,&FCTL1 : Reset write bit
XOR #(Fxkey+Lock),&FCTL3 : Change lock bit to 1
; Enable those interrupt sources that should be accepted
The BUSY bit can be tested before the write to the flash memory module is
done, or after a write (program) starts:
- For flash memory locations that hold data, it is a good practice to test the
BUSY bit before the write is executed. This has some time benefits, since
the write process is executed via the flash memory timing generator with-
out further CPU intervention. It is important that the clock source remains
active until BUSY is reset by the flash memory hardware.
The power or clock management, responsible for entering low-power
modes, has to make sure that it does not switch off the clock source used
by the flash controller.
- For flash memory blocks that hold program code, it is a good practice to
test the BUSY bit after the write is executed. The program can only pro-
ceed if the module can be accessed again. No special attention is needed
during execution of software code. Every write to the flash memory mod-
ule has to leave the programming cycle with the BUSY bit reset.
Testing the BUSY bit before writing to a flash memory block that holds pro-
gram code ensures that the active program will not access the flash
memory module. Two types of access are visible: execute program code,
or read and write data on this flash memory module.