PIC18F242 MICROCHIP [Microchip Technology], PIC18F242 Datasheet - Page 63

• Manufacturer Part Number: PIC18F242
• Description: 28/40-pin High Performance, Enhanced FLASH Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

5.5
The minimum programming block is 4 words or 8 bytes.
Word or byte programming is not supported.
Table Writes are used internally to load the holding reg-
isters needed to program the FLASH memory. There
are 8 holding registers used by the Table Writes for
programming.
Since the Table Latch (TABLAT) is only a single byte,
the TBLWT instruction has to be executed 8 times for
each programming operation. All of the Table Write
FIGURE 5-5:
5.5.1
The sequence of events for programming an internal
program memory location should be:
1.
2.
3.
4.
5.
6.
7.
8.
9.
© 2006 Microchip Technology Inc.
TBLPTR = xxxxx0
Read 64 bytes into RAM.
Update data values in RAM as necessary.
Load Table Pointer with address being erased.
Do the row erase procedure.
Load Table Pointer with address of first byte
being written.
Write the first 8 bytes into the holding registers
with auto-increment (TBLWT*+ or TBLWT+*).
Set EEPGD bit to point to program memory,
clear the CFGS bit to access program memory,
and set WREN to enable byte writes.
Disable interrupts.
Write 55h to EECON2.
Writing to FLASH Program
Memory
FLASH PROGRAM MEMORY WRITE
SEQUENCE
Holding Register
8
TABLE WRITES TO FLASH PROGRAM MEMORY
TBLPTR = xxxxx1
Holding Register
8
Program Memory
TBLPTR = xxxxx2
Write Register
TABLAT
operations will essentially be short writes, because only
the holding registers are written. At the end of updating
8 registers, the EECON1 register must be written to, 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 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 for byte or word operations.
10. Write AAh to EECON2.
11. Set the WR bit. This will begin the write cycle.
12. The CPU will stall for duration of the write (about
13. Re-enable interrupts.
14. Repeat steps 6-14 seven times, to write
15. Verify the memory (Table Read).
This procedure will require about 18 ms to update one
row of 64 bytes of memory. An example of the required
code is given in Example 5-3.
Note:
Holding Register
2 ms using internal timer).
64 bytes.
8
Before setting the WR bit, the table pointer
address needs to be within the intended
address range of the 8 bytes in the holding
registers.
TBLPTR = xxxxx7
PIC18FXX2
Holding Register
DS39564C-page 61
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