PIC18F45J10 FAMILY
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.
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.
Note:
Unlike previous devices, the PIC18F45J10
family of devices does not reset the holding
registers after a write occurs. The holding
registers must be cleared or overwritten
before a programming sequence.
Since the Table Latch (TABLAT) is only a single byte, the
TBLWTinstruction 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.
In order to maintain the endurance of the
cells, each Flash byte should not be
programmed more then twice between
erase operations. Either a Bulk or Row
Erase of the target row is required before
attempting to modify the contents a third
time.
The long write is necessary for programming the inter-
nal Flash. Instruction execution is halted while in a long
write cycle. The long write will be terminated by the
internal programming timer.
FIGURE 7-5:
TABLE WRITES TO FLASH PROGRAM MEMORY
TABLAT
Write Register
8
8
8
8
TBLPTR = xxxxx0
TBLPTR = xxxxx1
TBLPTR = xxxxx2
TBLPTR = xxxx3F
Holding Register
Holding Register
Holding Register
Holding Register
Program Memory
5. Write 55h to EECON2.
6. Write 0AAh to EECON2.
7.5.1
FLASH PROGRAM MEMORY WRITE
SEQUENCE
7. Set the WR bit. This will begin the write cycle.
The sequence of events for programming an internal
program memory location should be:
8. The CPU will stall for duration of the write (about
2 ms using internal timer).
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”).
9. Re-enable interrupts.
10. Verify the memory (table read).
An example of the required code is shown in
Example 7-3.
2. Write the 64 bytes into the holding registers with
auto-increment.
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.
3. Set the EECON1 register for the write operation:
• set WREN to enable byte writes.
4. Disable interrupts.
© 2009 Microchip Technology Inc.
DS39682E-page 77
MICROCHIP [ MICROCHIP ]
