PIC18LF2XK22 Datasheet, PDF(19/42 Page) Microchip Technology – Flash Memory Programming Specification

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PIC18LF2XK22 Datasheet, PDF (19/42 Pages) Microchip Technology – Flash Memory Programming Specification

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PIC18(L)F2XK22/4XK22

3.2.1 MODIFYING CODE MEMORY

The previous programming example assumed that the

device has been Bulk Erased prior to programming

(see Section 3.1.1 âHigh-Voltage ICSP Bulk 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.

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

used to initiate a write sequence.

TABLE 3-6: MODIFYING CODE MEMORY

4-bit

Command

Data Payload

Core Instruction

Step 1: Direct access to code memory.

0000

8E A6

9C A6

BSF EECON1, EEPGD

BCF EECON1, CFGS

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

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

Step 4: Enable memory writes and setup an erase.

<Addr[21:16]>

TBLPTRU

<Addr[8:15]>

TBLPTRH

<Addr[7:0]>

TBLPTRL

0000

84 A6

88 A6

BSF EECON1, WREN

BSF EECON1, FREE

Step 5: Initiate erase.

0000

88 A6

BSF

82 A6

BSF

00 00

NOP

00 00

NOP

Step 6: Poll WR bit. Repeat until bit is clear.

EECON1, FREE

EECON1, WR

Erase starts on the 4th clock of this instruction

0000

50 A6

6E F5

00 00

MOVF EECON1, W, 0

MOVWF TABLAT

NOP

Shift out data(1)

Step 7: Load write buffer. The correct bytes will be selected based on the Table Pointer.

0000

1101

â¢

1111

0000

0E <Addr[21:16]>

6E F8

0E <Addr[8:15]>

6E F7

0E <Addr[7:0]>

6E F6

â¢

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 as many times as necessary to fill the write buffer

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 6, where the Address Pointer is incremented by the appropriate number of bytes

(see Table 3-4) at each iteration of the loop. The write cycle must be repeated enough times to completely rewrite the contents of the

erase buffer.

Step 8: Disable writes.

0000

94 A6

BCF EECON1, WREN

ï£ 2010 Microchip Technology Inc.

Advance Information

DS41398B-page 19

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