15.3.1 NVMREG Read Operation
To read a NVM location using the NVMREG interface, the user must:
- Clear the NVMREGS bit if the user intends to access program memory locations, or set NMVREGS if the user intends to access User ID or configuration locations.
- Write the desired address into the NVMADRH:NVMADRL register pair.
- Set the RD bit to initiate the read.
Once the read control bit is set, the CPU operation is suspended during the read, and resumes immediately after. The data is available in the very next cycle, in the NVMDATH:NVMDATL register pair; therefore, it can be read as two bytes in the following instructions.
NVMDATH:NVMDATL register pair will hold this value until another read or until it is written to by the user.
Upon completion, the RD bit is cleared by hardware.
Program Memory read
* This code block will read 1 word of program
* memory at the memory address:
PROG_ADDR_HI : PROG_ADDR_LO
* data will be returned in the variables:
* PROG_DATA_HI, PROG_DATA_LO
BANKSEL NVMADRL ; Select Bank for NVMCON registers
MOVLW PROG_ADDR_LO
MOVWF NVMADRL ; Store LSB of address
MOVLW PROG_ADDR_HI
MOVWF NVMADRH ; Store MSB of address
BCF NVMCON1,NVMREGS ; Do not select Configuration Space
BSF NVMCON1,RD ; Initiate read
MOVF NVMDATL,W ; Get LSB of word
MOVWF PROG_DATA_LO ; Store in user location
MOVF NVMDATH,W ; Get MSB of word
MOVWF PROG_DATA_HI ; Store in user location