Datasheet

© 2009 Microchip Technology Inc. DS41203E-page 81
PIC16F688
9.1.4 READING THE FLASH PROGRAM
MEMORY
To read a program memory location, the user must
write two bytes of the address to the EEADR and
EEADRH registers, set the EEPGD control bit of the
EECON1 register, and then set control bit RD of the
EECON1 register. Once the read control bit is set, the
program memory Flash controller will use the second
instruction cycle to read the data. This causes the sec-
ond instruction immediately following the “
BSF
EECON1,RD
” instruction to be ignored. The data is
available in the very next cycle, in the EEDAT and
EEDATH registers; therefore, it can be read as two
bytes in the following instructions.
EEDAT and EEDATH registers will hold this value until
another read or until it is written to by the user (during
a write operation).
EXAMPLE 9-3: FLASH PROGRAM READ
Note 1: The two instructions following a program
memory read are required to be NOP’s.
This prevents the user from executing a
two-cycle instruction on the next
instruction after the RD bit is set.
2: If the WR bit is set when EEPGD = 1, it
will be immediately reset to ‘0’ and no
operation will take place.
BANKSEL EEADR ;
MOVLW MS_PROG_EE_ADDR ;
MOVWF EEADRH ;MS Byte of Program Address to read
MOVLW LS_PROG_EE_ADDR ;
MOVWF EEADR ;LS Byte of Program Address to read
BANKSEL EECON1 ;
BSF EECON1, EEPGD ;Point to PROGRAM memory
BSF EECON1, RD ;EE Read
;
;First instruction after BSF EECON1,RD executes normally
NOP
NOP ;Any instructions here are ignored as program
;memory is read in second cycle after BSF EECON1,RD
;
BANKSEL EEDAT ;
MOVF EEDAT, W ;W = LS Byte of Program Memory
MOVWF LOWPMBYTE ;
MOVF EEDATH, W ;W = MS Byte of Program EEDAT
MOVWF HIGHPMBYTE ;
BCF STATUS, RP1 ;Bank 0
Required
Sequence