PIC16F87 datasheet(32/230 Pages) MICROCHIP

32 / 230 page

PIC16F87/88

DS30487D-page 32

 2002-2013 Microchip Technology Inc.

3.7

Writing to Flash Program Memory

Flash program memory may only be written to if the

destination address is in a segment of memory that is

not write-protected, as defined in bits WRT1:WRT0 of

the device Configuration Word (Register 15-1). Flash

program memory must be written in four-word blocks.

A block consists of four words with sequential

addresses, with a lower boundary defined by an

address, where EEADR<1:0> = 00. At the same time,

all block writes to program memory are done as write-

only operations. The program memory must first be

erased. The write operation is edge-aligned and cannot

occur across boundaries.

To write to the program memory, the data must first be

loaded into the buffer registers. There are four 14-bit

buffer registers and they are addressed by the low

2 bits of EEADR.

The following sequence of events illustrate how to

perform a write to program memory:

• Set the EEPGD and WREN bits in the EECON1

• Clear the FREE bit in EECON1

• Write address to EEADRH:EEADR

• Write data to EEDATH:EEDATA

• Write 55 to EECON2

• Write AA to EECON2

• Set WR bit in EECON1

The user must follow the same specific sequence to

initiate the write for each word in the program block

by writing each program word in sequence (00, 01,

, 11).

There are 4 buffer register words and all four locations

MUST be written to with correct data.

After

the

“BSF

EECON1,

”

instruction,

EEADR

 xxxxxx11, then a short write will occur.

This short write only transfers the data to the buffer

1cycle.

After

the

“BSF

EECON1,

”

instruction,

EEADR = xxxxxx11, then a long write will occur. This

will

simultaneously

transfer

the

data

from

EEDATH:EEDATA to the buffer registers and begin the

write of all four words. The processor will execute the

next instruction and then ignore the subsequent

instruction. The user should place NOP instructions into

the second words. The processor will then halt internal

operations for typically 2 msec in which the write takes

place. This is not Sleep mode, as the clocks and

peripherals will continue to run. After the write cycle,

the processor will resume operation with the 3rd

instruction after the EECON1 write instruction.

After each long write, the 4 buffer registers will be reset

to 3FFF.

FIGURE 3-1:

BLOCK WRITES TO FLASH PROGRAM MEMORY

Program Memory

Buffer Register

EEADR<1:0>

= 00

Buffer Register

EEADR<1:0>

= 01

Buffer Register

EEADR<1:0>

= 10

Buffer Register

EEADR<1:0>

= 11

EEDATA

EEDATH

First word of block

to be written

to Flash

automatically

after this word

is written

transferred

All buffers are

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