Flash Memory Operation

5.3.4Flash Memory Access During Write or Erase

When any write or any erase operation is initiated from RAM and while BUSY=1, the CPU may not read or write to or from any flash location. Otherwise, an access violation occurs, ACCVIFG is set, and the result is unpredictable. Also if a write to flash is attempted with WRT=0, the ACCVIFG interrupt flag is set, and the flash memory is unaffected.

When a byte/word write or any erase operation is initiated from within flash memory, the flash controller returns op-code 03FFFh to the CPU at the next instruction fetch. Op-code 03FFFh is the JMP PC instruction. This causes the CPU to loop until the flash operation is finished. When the operation is finished and BUSY=0, the flash controller allows the CPU to fetch the proper op-code and program execution resumes.

The flash access conditions while BUSY=1 are listed in Table 5−3.

Table 5−3. Flash Access While BUSY = 1

Flash

Flash

WAIT

Result

Operation

Access

 

 

 

 

 

 

 

Read

0

ACCVIFG = 0. 03FFFh is the value read

Any erase, or

Write

0

ACCVIFG = 1. Write is ignored

Byte/word write

Instruction

0

ACCVIFG = 0. CPU fetches 03FFFh. This

 

 

fetch

 

is the JMP PC instruction.

 

 

 

 

 

Any

0

ACCVIFG = 1, LOCK = 1

 

Read

1

ACCVIFG = 0, 03FFFh is the value read

Block write

Write

1

ACCVIFG = 0, Write is ignored

 

Instruction

1

ACCVIFG = 1, LOCK = 1

 

fetch

 

 

 

 

 

 

All interrupt sources should be disabled before initiating any flash operation. If an enabled interrupt were to occur during a flash operation, the CPU would fetch 03FFFh as the address of the interrupt service routine. The CPU would then execute the JMP PC instruction while BUSY=1. When the flash operation finished, the CPU would begin executing code at address 03FFFh, not the correct address for interrupt service routine.

5-14

Flash Memory Controller

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Texas Instruments MSP430x1xx manual Flash Memory Access During Write or Erase, 3. Flash Access While Busy =, Result

MSP430x1xx specifications

The Texas Instruments MSP430x1xx series is a family of ultra-low-power microcontrollers that are highly regarded in the embedded systems community for their versatility and performance. Designed for applications ranging from portable instrumentation to low-power industrial devices, the MSP430x1xx combines flexibility and efficiency with advanced features tailored for energy-sensitive applications.

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