12.1.1.6 Reading the Program Flash Memory

The TBLRD instruction retrieves data from program memory at the TBLPTR location and places it into the TABLAT SFR register. Table reads from program memory are performed one byte at a time. In addition, TBLPTR can be modified automatically for the next table read operation.

The CPU operation is suspended during the read, and it resumes immediately after. From the user point of view, TABLAT is valid in the next instruction cycle.

The internal program memory is typically organized by words. The Least Significant bit of the address selects between the high and low bytes of the word. Figure 12-4 shows the interface between the internal program memory and the TABLAT.

Figure 12-4. Reads from Program Flash Memory

Figure 12-5. Program Flash Memory Read Flowchart

Reading a Program Flash Memory Word

   MOVLW   CODE_ADDR_UPPER    ; Load TBLPTR with the base   
   MOVWF   TBLPTRU            ; address of the word
   MOVLW   CODE_ADDR_HIGH
   MOVWF   TBLPTRH
   MOVLW   CODE_ADDR_LOW
   MOVWF   TBLPTRL
READ_WORD:
   TBLRD*+                    ; read into TABLAT and increment
   MOVF    TABLAT, W          ; get data
   MOVWF   WORD_EVEN
   TBLRD*+                    ; read into TABLAT and increment
   MOVFW   TABLAT, W          ; get data
   MOVF    WORD_ODD