Datasheet

 2009-2011 Microchip Technology Inc. DS39960D-page 117
PIC18F87K22 FAMILY
7.5 Writing to Flash Program Memory
The programming blocks are:
• PIC18FX5K22 and PIC18FX6K22 – 32 words or
64 bytes
• PIC18FX7K22 – 64 words or 128 bytes
Word or byte programming is not supported.
Table writes are used internally to load the holding
registers needed to program the Flash memory. The
number of holding registers used for programming by
the table writes are:
• PIC18FX5K22 and PIC18FX6K22 – 64
• PIC18FX7K22 – 128
Since the Table Latch (TABLAT) is only a single byte, the
TBLWT instruction may need to be executed 64 times for
each programming operation. All of the table write oper-
ations will essentially be short writes because only the
holding registers are written. At the end of updating the
64 or 128 holding registers, the EECON1 register must
be written to in order to start the programming operation
with a long write.
The long write is necessary for programming the
internal Flash. Instruction execution is halted while in a
long write cycle. The long write is 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.
FIGURE 7-5: TABLE WRITES TO FLASH PROGRAM MEMORY
Note: The default value of the holding registers
on device Resets, and after write opera-
tions, 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 64 or 128 holding registers before
executing a write operation.
TABLAT
TBLPTR = xxxx3FTBLPTR = xxxxx1TBLPTR = xxxxx0
Write Register
TBLPTR = xxxxx2
Program Memory
Holding Register Holding Register Holding Register Holding Register
8
8 8 8