PIC18F97J60_11 Datasheet, PDF (111/492 Pages) Microchip Technology – 64/80/100-Pin, High-Performance, 1-Mbit Flash Microcontrollers with Ethernet

PIC18F97J60 FAMILY
7.5 Writing to Flash Program Memory
The minimum programming block is 32 words or
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 64 holding registers used by the table writes for
programming.
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
operations will essentially be short writes because only
the holding registers are written. At the end of updating
the 64 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 will be terminated by
the internal programming timer.
An on-chip timer controls the write time. The
write/erase voltages are generated by an on-chip
charge pump, rated to operate over most of the
voltage range of the device. See Parameter D132B
(VPEW) for specific limits.
Note 1: Unlike previous PIC MCU devices,
members of the PIC18F97J60 family do
not reset the holding registers after a
write occurs. The holding registers must
be cleared or overwritten before a
programming sequence.
2: To maintain the endurance of the pro-
gram memory cells, each Flash byte
should not be programmed more than
one time between erase operations.
Before attempting to modify the contents
of the target cell a second time, a Row
Erase of the target row, or a Bulk Erase of
the entire memory, must be performed.
FIGURE 7-5:
TABLE WRITES TO FLASH PROGRAM MEMORY
TABLAT
Write Register
8
8
8
TBLPTR = xxxxx0
TBLPTR = xxxxx1
TBLPTR = xxxxx2
Holding Register
Holding Register
Holding Register
8
TBLPTR = xxxx3F
Holding Register
Program Memory
7.5.1
FLASH PROGRAM MEMORY WRITE
SEQUENCE
The sequence of events for programming an internal
program memory location should be:
1. If the section of program memory to be written to
has been programmed previously, then the
memory will need to be erased before the write
occurs (see Section 7.4.1 “Flash Program
Memory Erase Sequence”).
2. Write the 64 bytes into the holding registers with
auto-increment.
3. Set the WREN bit to enable byte writes.
4. Disable interrupts.
5. Write 55h to EECON2.
6. Write AAh to EECON2.
7. Set the WR bit. This will begin the write cycle.
8. The CPU will stall for the duration of the write.
9. Re-enable interrupts.
10. Verify the memory (table read).
An example of the required code is shown in
Example 7-3.
Note:
Before setting the WR bit, the Table
Pointer address needs to be within the
intended address range of the 64 bytes in
the holding register.
 2011 Microchip Technology Inc.
DS39762F-page 111