20.5 Self programming

The Flash in Tiny104 does not support Read-While-Write, and cannot be read during an erase or write operation. Therefore, the CPU will halt execution.

The device provides a Self-Programming mechanism for downloading and uploading program code by the MCU itself. Only WORD_WRITE and PAGE_ERASE commands are supported in self-programming. The CPU can execute Page Erase and Word Write in the NVM code memory section to perform programming operations.

Note: The user needs to add two NOP operations after the ST operation that triggers the self-programming to ensure correct CPU operation.
Table 20-9. Example code for self-programming:
Assembly Code Example

The sequence for entering self-programming mode is given below (r19 can be any register): 

              
;  set CCP               
ldi            r19, 0xe7               
out          CCP, r19

The software then has to perform the desired self-programming operation within 4 clock cycles. Example of the complete code to perform page erase: 

;  erase page               
;  set the page address pointer               
ldi            ZL, 0xE1               
ldi            ZH, 0x43               
;  set NVMCMD to page erase               
ldi            temp, 0b011000               
out          NVMCMD, temp               
;  set CCP to enter program mode               
ldi            r19, 0xe7               
out          CCP, r19               
; trigger the erase operation (within four clock cycles)               
ldi            temp, 0x00               
st            Z+, temp               
; required for proper CPU halting               
nop               
nop