PIC16F685-ESLASHSS datasheet(125/306 Pages) MICROCHIP

125 / 306 page

DS41262E-page 123

PIC16F631/677/685/687/689/690

10.1.4

READING THE FLASH PROGRAM

MEMORY (PIC16F685/PIC16F689/

PIC16F690)

To read a program memory location, the user must

write the Least and Most Significant address bits to the

EEADR and EEADRH registers, set the EEPGD con-

trol bit of the EECON1 register, and then set control bit

RD. Once the read control bit is set, the program mem-

ory Flash controller will use the second instruction

cycle to read the data. This causes the second instruc-

tion 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.

EXAMPLE 10-3:

FLASH PROGRAM READ

Note 1: The two instructions following a program

memory read are required to be NOPs.

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

;

MOVF

MS_PROG_EE_ADDR, W

;

MOVWF

EEADRH

;MS Byte of Program Address to read

MOVF

LS_PROG_EE_ADDR, W

;

MOVWF

EEADR

;LS Byte of Program Address to read

BANKSEL EECON1

;

BSF

EECON1, EEPGD

;Point to PROGRAM memory

BSF

EECON1, RD

;EE Read

;

NOP

;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

;

BANKSEL 0x00

;Bank 0

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