PIC18F87K90 Datasheet, PDF (115/566 Pages) Microchip Technology – 64/80-Pin, High-Performance Microcontrollers with LCD Driver and nanoWatt XLP Technology

PIC18F87K90 FAMILY
7.5 Writing to Flash Program Memory
The programming block is 32 words or 64 bytes for
PIC18FX5K90 and PIC18FX6K90 devices, and
64 words or 128 bytes for PIC18FX7K90 devices.
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 for PIC18FX5K90 and
PIC18FX6K90 devices and 128 holding registers for
PIC18FX7K90 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 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 inter-
nal 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.
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 64 or 128 holding
registers before executing a write operation.
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. Read the 64 or 128 bytes into RAM.
2. Update the data values in RAM as necessary.
3. Load the Table Pointer register with the address
being erased.
4. Execute the row erase procedure.
5. Load the Table Pointer register with the address
of the first byte being written.
6. Write the 64 or 128 bytes into the holding
registers with auto-increment.
7. Set the EECON1 register for the write operation:
• Set the EEPGD bit to point to program memory
• Clear the CFGS bit to access program memory
• Set WREN to enable byte writes
8. Disable the interrupts.
9. Write 0x55 to EECON2.
10. Write 0xAA to EECON2.
11. Set the WR bit. This will begin the write cycle.
The CPU will stall for duration of the write for TIW
(see parameter D133A).
12. Re-enable the interrupts.
13. Verify the memory (table read).
An example of the required code is shown in
Example 7-3 on the following page.
Note:
Before setting the WR bit, the Table
Pointer address needs to be within the
intended address range of the 64 or
128 bytes in the holding register.
Note:
Self-write execution to Flash and
EEPROM memory cannot be done while
running in LP Oscillator mode (Low-Power
mode). Therefore, executing a self-write
will put the device into High-Power mode.
 2010 Microchip Technology Inc.
Preliminary
DS39957B-page 115