PIC16F877ATISLASHML datasheet(38/234 Pages) MICROCHIP

38 / 234 page

PIC16F87XA

DS39582B-page 36

 2003 Microchip Technology Inc.

3.5

Reading 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 (EECON1<7>) and

then set control bit RD (EECON1<0>). Once the read

control bit is set, the program memory Flash controller

will use the next two instruction cycles to read the data.

This causes these two instructions immediately follow-

ing the “BSF

EECON1,RD

” instruction to be ignored.

The data is available in the very next cycle in the

EEDATA and EEDATH registers; therefore, it can be

read as two bytes in the following instructions. EEDATA

and EEDATH registers will hold this value until another

read or until it is written to by the user (during a write

operation).

EXAMPLE 3-3:

FLASH PROGRAM READ

BSF

STATUS, RP1

;

BCF

STATUS, RP0

; Bank 2

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

BSF

STATUS, RP0

; Bank 3

BSF

EECON1, EEPGD

; Point to PROGRAM memory

BSF

EECON1, RD

; EE Read

;

NOP

; Any instructions here are ignored as program

; memory is read in second cycle after BSF EECON1,RD

;

BCF

STATUS, RP0

; Bank 2

MOVF

EEDATA, W

; W = LS Byte of Program EEDATA

MOVWF

DATAL

;

MOVF

EEDATH, W

; W = MS Byte of Program EEDATA

MOVWF

DATAH

;

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