PIC24F04KA201 datasheet(48/224 Pages) MICROCHIP

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PIC24F04KA201 FAMILY

DS39937B-page 46

Preliminary

5.5.1

PROGRAMMING ALGORITHM FOR

FLASH PROGRAM MEMORY

The user can program one row of Flash program

memory at a time by erasing the programmable row.

The general process is:

Read

row

program

memory

(32 instructions) and store in data RAM.

Update the program data in RAM with the

desired new data.

Erase a row (see Example 5-1):

Set the NVMOP bits (NVMCON<5:0>) to

‘011000’ to configure for row erase. Set the

ERASE

(NVMCON<6>)

and

WREN

(NVMCON<14>) bits.

Write the starting address of the block to be

erased into the TBLPAG and W registers.

Write 55h to NVMKEY.

Write AAh to NVMKEY.

Set the WR bit (NVMCON<15>). The erase

cycle begins and the CPU stalls for the

duration of the erase cycle. When the erase is

done, the WR bit is cleared automatically.

Write the first 32 instructions from data RAM into

the program memory buffers (see Example 5-1).

Write the program block to Flash memory:

a) Set the NVMOP bits to ‘011000’ to

configure for row programming. Clear the

ERASE bit and set the WREN bit.

b) Write 55h to NVMKEY.

Write AAh to NVMKEY.

Set the WR bit. The programming cycle

begins and the CPU stalls for the duration of

the write cycle. When the write to Flash

memory is done, the WR bit is cleared

automatically.

For protection against accidental operations, the write

initiate sequence for NVMKEY must be used to allow

any erase or program operation to proceed. After the

programming command has been executed, the user

must wait for the programming time until programming

is complete. The two instructions following the start of

the programming sequence should be NOPs, as

displayed in Example 5-5.

EXAMPLE 5-1:

ERASING A PROGRAM MEMORY ROW – ASSEMBLY LANGUAGE CODE

; Set up NVMCON for row erase operation

MOV

#0x4058, W0

;

MOV

W0, NVMCON

; Initialize NVMCON

; Init pointer to row to be ERASED

MOV

#tblpage(PROG_ADDR), W0

;

MOV

W0, TBLPAG

; Initialize PM Page Boundary SFR

MOV

#tbloffset(PROG_ADDR), W0

; Initialize in-page EA[15:0] pointer

TBLWTL

W0, [W0]

; Set base address of erase block

DISI

; Block all interrupts

for next 5 instructions

MOV

#0x55, W0

MOV

W0, NVMKEY

; Write the 55 key

MOV

#0xAA, W1

;

MOV

W1, NVMKEY

; Write the AA key

BSET

NVMCON, #WR

; Start the erase sequence

NOP

; Insert two NOPs after the erase

NOP

; command is asserted

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