PIC18F44J50-I/ML【PDF 6/32 页】IC PIC MCU FLASH 16K 2V 44-QFN

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PIC18F2XJXX/4XJXX FAMILY

DS39687E-page 14

2009 Microchip Technology Inc.

3.2.1

MODIFYING CODE MEMORY

The previous programming example assumed that the

device had been Bulk Erased prior to programming. 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 “Verify Code Memory and Configura-

tion Word”) 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 code sequence is shown in

Table 3-4.

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

used to initiate a write sequence.

3.2.2

CONFIGURATION WORD

PROGRAMMING

Since the Flash Configuration Words are stored in

program memory, they are programmed as if they were

program data. Refer to Section 3.2 “Code Memory

Programming” and Section 3.2.1 “Modifying Code

Memory” for methods and examples on programming

or modifying program memory. See also Section 5.0

“Configuration Word” for additional information on

the Configuration Words.

TABLE 3-4:

MODIFYING CODE MEMORY

4-Bit

Command

Data Payload

Core Instruction

Step 1: 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

<Addr[21:16]>

MOVWF

TBLPTRU

MOVLW

<Addr[8:15]>

MOVWF

TBLPTRH

MOVLW

<Addr[7:0]>

MOVWF

TBLPTRL

Step 2: Read and modify code memory (see Section 4.1 “Read Code Memory”).

Step 3: Enable memory writes and set up an erase.

0000

84 A6

88 A6

BSF

EECON1, WREN

BSF

EECON1, FREE

Step 4: Initiate erase.

0000

82 A6

00 00

BSF

EECON1, WR

NOP - hold PGC high for time P10.

Step 5: 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 write operation 30 more times to fill the write buffer

Write 2 bytes and start programming.

NOP - hold PGC high for time P9.

Step 6: Repeat Step 5 for a total of 16 times (if rewriting the entire 1024 bytes of the erase page size).

Step 7: To continue modifying data, repeat Steps 1 through 5, where the Address Pointer is incremented by 1024 bytes at each

iteration of the loop.

Step 8: Disable writes.

0000

94 A6

BCF

EECON1, WREN

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