PIC16F688_09 datasheet(83/204 Pages) MICROCHIP

83 / 204 page

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

the

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

;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

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