PIC18FXXK80 Datasheet, PDF(25/52 Page) Microchip Technology – Flash Microcontroller Programming Specification

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PIC18FXXK80 Datasheet, PDF (25/52 Pages) Microchip Technology – Flash Microcontroller Programming Specification

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PIC18FXXK80 FAMILY

3.2.2 MODIFYING CODE MEMORY

The previous programming example assumed that the

device had been erased entirely prior to programming

(see Section 3.1.1 âICSP Block Eraseâ). It may be the

case, however, that the user wishes to modify only a

section of an already programmed device.

The appropriate number of bytes required for the erase

buffer must be read out of code memory (as described

in Section 4.2 âVerify Code Memory and ID Loca-

tionsâ) and buffered. Modifications can be made on this

buffer. Then, the block of code memory that was read

out must be erased and rewritten with the modified data

(see Section 3.2.1 âProgrammingâ).

The WREN bit must be set if the WR bit in EECON1 is

used to initiate a write sequence.

TABLE 3-12: MODIFYING CODE MEMORY

4-Bit

Command

Data Payload

Core Instruction

Step 1: Direct access to code memory.

Step 2: Read and modify code memory (see Section 4.1 âRead Code Memory, ID Locations and Configuration Bitsâ).

0000

8E 7F

9C 7F

BSF EECON1, EEPGD

BCF EECON1, CFGS

Step 3: Set the Table Pointer for the block to be erased.

0000

0E <Addr[21:16]>

6E F8

0E <Addr[8:15]>

6E F7

0E <Addr[7:0]>

6E F6

MOVLW

MOVWF

MOVLW

MOVWF

MOVLW

MOVWF

<Addr[21:16]>

TBLPTRU

<Addr[8:15]>

TBLPTRH

<Addr[7:0]>

TBLPTRL

Step 4: Enable memory writes and set up an erase.

0000

84 7F

88 7F

BSF EECON1, WREN

BSF EECON1, FREE

Step 5: Initiate erase.

0000

82 7F

00 00

BSF EECON1, WR

NOP - hold PGC high for time P9 and low for time P10.

Step 6: Direct access to configuration memory.

0000

8E 7F

8C 7F

84 7F

BSF EECON1, EEPGD

BSF EECON1, CFGS

BSF EECON1, WREN

Step 7: Direct access to code memory and enable writes.

0000

8E 7F

9C 7F

BSF EECON1, EEPGD

BCF EECON1, CFGS

Step 8: Load write buffer. The correct bytes will be selected based on the Table Pointer.

0000

1101

1111

0000

0E <Addr[21:16]>

6E F8

0E <Addr[8:15]>

6E F7

0E <Addr[7:0]>

6E F6

00 00

MOVLW <Addr[21:16]>

MOVWF TBLPTRU

MOVLW <Addr[8:15]>

MOVWF TBLPTRH

MOVLW <Addr[7:0]>

MOVWF TBLPTRL

Write 2 bytes and post-increment address by 2.

Repeat 31 times

Write 2 bytes and start programming.

NOP - hold PGC high for time P9 and low for time P10.

To continue modifying data, repeat Steps 2 through 8, where the Address Pointer is incremented by 64 bytes at each iteration of the

loop.

Step 9: Disable writes.

0000

94 7F

BCF EECON1, WREN

ï£ 2011 Microchip Technology Inc.

DS39972B-page 25

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