Datasheet

PIC16F882/883/884/886/887
DS40001291H-page 116  2006-2015 Microchip Technology Inc.
10.2 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 WRT<1:0> of the
Configuration Word Register 2. Flash program memory
must be written in 8-word blocks (4-word blocks for 4K
memory devices). See Figures 10-2 and 10-3 for more
details. A block consists of eight words with sequential
addresses, with a lower boundary defined by an
address, where EEADR<2:0> = 000. All block writes to
program memory are done as 16-word erase by 8-word
write operations. The write operation is edge-aligned
and cannot occur across boundaries.
To write program data, it must first be loaded into the
buffer registers (see Figure 10-2). This is accomplished
by first writing the destination address to EEADR and
EEADRH and then writing the data to EEDATA and
EEDATH. After the address and data have been set up,
then the following sequence of events must be
executed:
1. Set the EEPGD control bit of the EECON1
register.
2. Write 55h, then AAh, to EECON2 (Flash
programming sequence).
3. Set the WR control bit of the EECON1 register.
All eight buffer register locations should be written to
with correct data. If less than eight words are being
written to in the block of eight words, then a read from
the program memory location(s) not being written to
must be performed. This takes the data from the pro-
gram location(s) not being written and loads it into the
EEDATA and EEDATH registers. Then the sequence of
events to transfer data to the buffer registers must be
executed.
To transfer data from the buffer registers to the program
memory, the EEADR and EEADRH must point to the last
location in the 8-word block (EEADR<2:0> = 111). Then
the following sequence of events must be executed:
1. Set the EEPGD control bit of the EECON1
register.
2. Write 55h, then AAh, to EECON2 (Flash
programming sequence).
3. Set control bit WR of the EECON1 register to
begin the write operation.
The user must follow the same specific sequence to
initiate the write for each word in the program block,
writing each program word in sequence (000, 001,
010, 011, 100, 101, 110, 111). When the write is
performed on the last word (EEADR<2:0> = 111), a
block of sixteen words is automatically erased and the
content of the 8-word buffer registers are written into
the program memory.
After the “BSF EECON1,WR” instruction, the processor
requires two cycles to set up the erase/write operation.
The user must place two NOP instructions after the WR
bit is set. Since data is being written to buffer registers,
the writing of the first seven words of the block appears
to occur immediately. The processor will halt internal
operations for the typical 4 ms, only during the cycle in
which the erase takes place (i.e., the last word of the
sixteen-word block erase). This is not Sleep mode as
the clocks and peripherals will continue to run. After the
8-word write cycle, the processor will resume operation
with the third instruction after the EECON1 write
instruction. The above sequence must be repeated for
the higher eight words.