PIC18F2220/2320/4220/4320
Since the Table Latch (TABLAT) is only a single byte,
6.5
Writing to Flash Program Memory
the TBLWT instruction has to be executed 8 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
8 registers, the EECON1 register must be written to, to
start the programming operation with a long write.
The programming block size 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.
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 6-5:
TABLE WRITES TO FLASH PROGRAM MEMORY
TABLAT
Write Register
8
8
8
8
TBLPTR = xxxxx0
TBLPTR = xxxxx2
TBLPTR = xxxxx7
Holding Register
TBLPTR = xxxxx1
Holding Register
Holding Register
Holding Register
Program Memory
8. Disable interrupts.
6.5.1
FLASH PROGRAM MEMORY WRITE
SEQUENCE
9. Write 55h to EECON2.
10. Write AAh to EECON2.
The sequence of events for programming an internal
program memory location should be:
11. Set the WR bit. This will begin the write cycle.
12. The CPU will stall for duration of the write (about
2 ms using internal timer).
1. Read 64 bytes into RAM.
2. Update data values in RAM as necessary.
3. Load Table Pointer with address being erased.
13. Execute a NOP.
14. Re-enable interrupts.
4. Do the row erase procedure (see Section 6.4.1
“Flash Program Memory Erase Sequence”).
15. Repeat steps 6-14 seven times, to write 64
bytes.
5. Load Table Pointer with address of first byte
being written.
16. 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 6-3.
6. Write the first 8 bytes into the holding registers
with auto-increment.
7. Set the EECON1 register for the write operation:
• set EEPGD bit to point to program
memory;
• clear the CFGS bit to access program
memory;
• set WREN bit to enable byte writes.
2003 Microchip Technology Inc.
DS39599C-page 77
MICROCHIP [ MICROCHIP ]
