33.3.8.3 User Row Programming

The user row programming feature allows programming new values to the user row (USERROW) on a locked device. To program with this functionality enabled, the next sequence must be followed:

  1. Enter the USERROW-Write key located in Table 33-5 by using the KEY instruction. See Table 33-5 for the USERROW-Write signature.
  2. Optional: Read the User Row Write Key Status (UROWWR) bit from the ASI Key Status (UPDI.ASI_KEY_STATUS) register to see if the key has been activated.
  3. Write the signature to the Reset Request (RSTREQ) bit in the ASI Reset Request (UPDI.ASI_RESET_REQ) register. This will issue a System Reset.
  4. Write 0x00 to the ASI Reset Request (UPDI.ASI_RESET_REQ) register to clear the System Reset.
  5. Read the Start User Row Programming (UROWSTART) bit from the ASI System Status (UPDI.ASI_SYS_STATUS) register.
  6. The user row programming can start when the UROWSTART bit is ‘1’. If UROWSTART is ‘0’, return to step 5.
  7. The data to be written to the User Row must first be written to a buffer in the RAM. The writable area in the RAM has a size of 64 bytes, and it is only possible to write user row data to the first 64 byte addresses of the RAM. Addressing outside this memory range will result in a nonexecuted write. The data will map 1:1 with the user row space when the data is copied into the user row upon completion of the programming sequence.
  8. When all the user row data has been written to the RAM, write the User Row Programming Done (UROWDONE) bit in the ASI System Control A (UPDI.ASI_SYS_CTRLA) register.
  9. Read the Start User Row Programming (UROWSTART) bit from the ASI System Status (UPDI.ASI_SYS_STATUS) register.
  10. The user row programming is completed when the UROWSTART bit is ‘0’. If the UROWSTART bit is ‘1’, return to step 9.
  11. Write to the User Row Write Key Status (UROWWR) bit in the ASI Key Status (UPDI.ASI_KEY_STATUS) register.
  12. Write the signature to the Reset Request (RSTREQ) bit in the ASI Reset Request (UPDI.ASI_RESET_REQ) register. This will issue a System Reset.
  13. Write 0x00 to the ASI Reset Request (UPDI.ASI_RESET_REQ) register to clear the System Reset.
  14. The user row programming is complete.

It is not possible to read back data from the RAM in this mode. Only writes to the first 64 bytes of the RAM are allowed.