C8051F970-A-GM Datasheet, PDF (67/454 Pages) Silicon Laboratories – Low Power Capacitive Sensing MCU with up to 32 kB of Flash

C8051F97x
10.2. Programming the Flash Memory
Writes to flash memory clear bits from logic 1 to logic 0, and can be performed on single byte locations. Flash
erasures set bits back to logic 1, and occur only on full pages. The write and erase operations are automatically
timed by hardware for proper execution; data polling to determine the end of the write/erase operation is not
required. Code execution is stalled during a flash write/erase operation.
The simplest means of programming the flash memory is through the C2 interface using programming tools
provided by Silicon Labs or a third party vendor. This is the only means for programming a non-initialized device.
To ensure the integrity of flash contents, it is strongly recommended that the on-chip supply monitor be enabled in
any system that includes code that writes and/or erases flash memory from software.
10.2.1. Flash Lock and Key Functions
Flash writes and erases by user software are protected with a lock and key function. The Flash Lock and Key
Register (FLKEY) must be written with the correct key codes, in sequence, before flash operations may be
performed. The key codes are: 0xA5, 0xF1. The timing does not matter, but the codes must be written in order. If
the key codes are written out of order, or the wrong codes are written, flash writes and erases will be disabled until
the next system reset. Flash writes and erases will also be disabled if a flash write or erase is attempted before the
key codes have been written properly. The flash lock resets after each write or erase; the key codes must be
written again before a following flash operation can be performed.
10.2.2. Flash Erase Procedure
The flash memory can be programmed by software using the MOVX write instruction with the address and data
byte to be programmed provided as normal operands. Before writing to flash memory using MOVX, flash write
operations must be enabled by: (1) setting the PSWE Program Store Write Enable bit in the PSCTL register to
logic 1 (this directs the MOVX writes to target flash memory); and (2) Writing the flash key codes in sequence to the
Flash Lock register (FLKEY). The PSWE bit remains set until cleared by software.
A write to flash memory can clear bits to logic 0 but cannot set them; only an erase operation can set bits to logic 1
in flash. A byte location to be programmed should be erased before a new value is written. Erase operation
applies to an entire page (setting all bytes in the page to 0xFF). To erase an entire page, perform the following
steps:
1. Disable interrupts (recommended).
2. Set the PSEE bit (register PSCTL).
3. Set the PSWE bit (register PSCTL).
4. Write the first key code to FLKEY: 0xA5.
5. Write the second key code to FLKEY: 0xF1.
6. Using the MOVX instruction, write a data byte to any location within the page to be erased.
7. Clear the PSWE and PSEE bits.
10.2.3. Flash Write Procedure
Flash bytes are programmed by software with the following sequence:
1. Disable interrupts (recommended).
2. Erase the flash page containing the target location, as described in Section 10.2.2.
3. Set the PSWE bit (register PSCTL).
4. Clear the PSEE bit (register PSCTL).
5. Write the first key code to FLKEY: 0xA5.
6. Write the second key code to FLKEY: 0xF1.
7. Using the MOVX instruction, write a single data byte to the desired location within the desired page.
8. Clear the PSWE bit.
Steps 5–7 must be repeated for each byte to be written. After flash writes are complete, PSWE should be cleared
so that MOVX instructions do not target program memory.
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