PIC12F1822 datasheet(95/410 Pages) MICROCHIP

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 2011-2012 Microchip Technology Inc.

DS41441C-page 95

PIC12(L)F1840

11.4

Modifying Flash Program Memory

When modifying existing data in a program memory

row, and data within that row must be preserved, it

must first be read and saved in a RAM image. Program

memory is modified using the following steps:

Load the starting address of the row to be mod-

ified.

Read the existing data from the row into a RAM

image.

Modify the RAM image to contain the new data

to be written into program memory.

Load the starting address of the row to be rewrit-

ten.

Erase the program memory row.

Load the write latches with data from the RAM

image.

Initiate a programming operation.

Repeat steps 6 and 7 as many times as required

to reprogram the erased row.

11.5

User ID, Device ID and

Configuration Word Access

Instead of accessing program memory or EEPROM

data memory, the User ID’s, Device ID/Revision ID and

Configuration Words can be accessed when CFGS = 1

in the EECON1 register. This is the region that would

be pointed to by PC<15> = 1, but not all addresses are

accessible. Different access may exist for reads and

writes. Refer to Table 11-2.

When read access is initiated on an address outside the

parameters listed in Table 11-2, the EEDATH:EEDATL

TABLE 11-2:

USER ID, DEVICE ID AND CONFIGURATION WORD ACCESS (CFGS = 1)

EXAMPLE 11-3:

CONFIGURATION WORD AND DEVICE ID ACCESS

Address

Function

Read Access

Write Access

8000h-8003h

User IDs

Yes

8006h

Device ID/Revision ID

Yes

8007h-8008h

Configuration Words 1 and 2

Yes

* This code block will read 1 word of program memory at the memory address:

PROG_ADDR_LO (must be 00h-08h) data will be returned in the variables;

PROG_DATA_HI, PROG_DATA_LO

BANKSEL

EEADRL

; Select correct Bank

MOVLW

PROG_ADDR_LO

;

MOVWF

EEADRL

; Store LSB of address

CLRF

EEADRH

; Clear MSB of address

BSF

EECON1,CFGS

; Select Configuration Space

BCF

INTCON,GIE

; Disable interrupts

BSF

EECON1,RD

; Initiate read

NOP

; Executed (See Figure 11-1)

NOP

; Ignored (See Figure 11-1)

BSF

INTCON,GIE

; Restore interrupts

MOVF

EEDATL,W

; Get LSB of word

MOVWF

PROG_DATA_LO

; Store in user location

MOVF

EEDATH,W

; Get MSB of word

MOVWF

PROG_DATA_HI

; Store in user location

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