PIC18F23K22 Datasheet, PDF (101/492 Pages) Microchip Technology – 28/40/44-Pin, Low-Power, High-Performance Microcontrollers with nanoWatt XLP Technology

PIC18(L)F2X/4XK22
6.5 Writing to Flash Program Memory
The programming block size is 64 bytes. Word or byte
programming is not supported.
Table writes are used internally to load the holding
registers needed to program the Flash memory. There
are only as many holding registers as there are bytes
in a write block (64 bytes).
Since the Table Latch (TABLAT) is only a single byte,
the TBLWT instruction needs to be executed 64 times
for each programming operation. All of the table write
operations will essentially be short writes because only
the holding registers are written. After all the holding
registers have been written, the programming
operation of that block of memory is started by
configuring the EECON1 register for a program
memory write and performing the long write sequence.
The long write is necessary for programming the
internal Flash. Instruction execution is halted during a
long write cycle. The long write will be terminated by
the internal programming timer.
The EEPROM on-chip timer controls the write time.
The write/erase voltages are generated by an on-chip
charge pump, rated to operate over the voltage range
of the device.
Note:
The default value of the holding registers on
device Resets and after write operations is
FFh. A write of FFh to a holding register
does not modify that byte. This means that
individual bytes of program memory may be
modified, provided that the change does not
attempt to change any bit from a ‘0’ to a ‘1’.
When modifying individual bytes, it is not
necessary to load all holding registers
before executing a long write operation.
FIGURE 6-5:
TABLE WRITES TO FLASH PROGRAM MEMORY
TABLAT
Write Register
8
8
8
TBLPTR = xxxx00
TBLPTR = xxxx01
TBLPTR = xxxx02
Holding Register
Holding Register
Holding Register
8
TBLPTR = xxxxYY⁽¹⁾
Holding Register
Program Memory
Note 1: YY = 3F for 64 byte write blocks.
6.5.1
FLASH PROGRAM MEMORY WRITE
SEQUENCE
The sequence of events for programming an internal
program memory location should be:
1. Read 64 bytes into RAM.
2. Update data values in RAM as necessary.
3. Load Table Pointer register with address being
erased.
4. Execute the block erase procedure.
5. Load Table Pointer register with address of first
byte being written.
6. Write the 64-byte block into the holding registers
with auto-increment.
7. Set the EECON1 register for the write operation:
• set EEPGD bit to point to program memory;
• clear the CFGS bit to access program memory;
• set WREN to enable byte writes.
8. Disable interrupts.
9. Write 55h to EECON2.
10. Write 0AAh to EECON2.
11. Set the WR bit. This will begin the write cycle.
12. The CPU will stall for duration of the write (about
2 ms using internal timer).
13. Re-enable interrupts.
14. Verify the memory (table read).
This procedure will require about 6 ms to update each
write block of memory. An example of the required code
is given in Example 6-3.
Note:
Before setting the WR bit, the Table
Pointer address needs to be within the
intended address range of the bytes in the
holding registers.
 2010 Microchip Technology Inc.
Preliminary
DS41412B-page 101