20.0 Internal Flash [T-Series Datasheet]

Flash Addresses

Internal flash is addressed by byte, but accessed by 32-bit values. That means that the first value is at address zero and the second is at address 4. (These are flash addresses—not to be confused with Modbus addresses.)

Following are some important flash addresses:

Reading

To read from flash, write the desired address to INTERNAL_FLASH_READ_POINTER and then read an even number of registers from INTERNAL_FLASH_READ:

Name	Start Address	Type	Access
INTERNAL_FLASH_READ_POINTER	61810	UINT32	R/W
INTERNAL_FLASH_READ_POINTER - Address: 61810 The address in internal flash that reads will start from. Data type: UINT32  (type index = 1) Readable and writable
INTERNAL_FLASH_READ	61812	UINT32	R
INTERNAL_FLASH_READ - Address: 61812 Data read from internal flash. Data type: UINT32  (type index = 1) Read-only

Writing and Erasing

Key

For a region to be written to or to be erased, the key for that region must be written to the INTERNAL_FLASH_KEY register:

Name	Start Address	Type	Access
INTERNAL_FLASH_KEY	61800	UINT32	R/W
INTERNAL_FLASH_KEY - Address: 61800 Sets the region of internal flash to which access is allowed. Data type: UINT32  (type index = 1) Readable and writable

The key prevents accidental overwrites. The value in INTERNAL_FLASH_KEY will be cleared when the Modbus packet that wrote it has been fully processed, so INTERNAL_FLASH_KEY must be written in the same packet that does INTERNAL_FLASH_WRITE or INTERNAL_FLASH_ERASE. The LJM Multiple Value functions simplify this.

Writing

To write to flash, the area to be written to must first be erased. Once erased, write the key for the desired region to INTERNAL_FLASH_KEY, write the desired address to INTERNAL_FLASH_WRITE_POINTER, and then write an even number of registers to INTERNAL_FLASH_WRITE:

Name	Start Address	Type	Access
INTERNAL_FLASH_WRITE_POINTER	61830	UINT32	R/W
INTERNAL_FLASH_WRITE_POINTER - Address: 61830 Address in internal flash where writes will begin. Data type: UINT32  (type index = 1) Readable and writable
INTERNAL_FLASH_WRITE	61832	UINT32	W
INTERNAL_FLASH_WRITE - Address: 61832 Data written here will be written to internal flash. This register is a buffer. Data type: UINT32  (type index = 1) Write-only This register is a Buffer Register

Erasing

Flash is erased 4 kB at a time. Erasing sets all bits to 1. To erase a 4 kB region, write the key for the desired region to INTERNAL_FLASH_KEY and the desired address to INTERNAL_FLASH_ERASE:

Name	Start Address	Type	Access
INTERNAL_FLASH_ERASE	61820	UINT32	W
INTERNAL_FLASH_ERASE - Address: 61820 Erases a 4k section of internal flash starting at the specified address. This register is a buffer. Data type: UINT32  (type index = 1) Write-only This register is a Buffer Register

The address will be rounded down to the nearest 4 kB boundary. Boundaries are easy to identify when the address is displayed in hexadecimal because the lower three digits will be zero. 4 kB is hexadecimal is 0x1000.

Endurance

Flash memory can only be erased so many times before bit errors will start to occur; it is important not to erase or write flash needlessly. Typical life of flash memory is at least 10,000 cycles.