Datasheet

 2010 Microchip Technology Inc. DS39622L-page 17
PIC18F2XXX/4XXX FAMILY
3.2 Code Memory Programming
Programming code memory is accomplished by first
loading data into the write buffer and then initiating a
programming sequence. The write and erase buffer
sizes, shown in Table 3-4, can be mapped to any
location of the same size, beginning at 000000h. The
actual memory write sequence takes the contents of
this buffer and programs the proper amount of code
memory that contains the Table Pointer.
The programming duration is externally timed and is
controlled by PGC. After a Start Programming
command is issued (4-bit command, ‘1111’), a NOP is
issued, where the 4th PGC is held high for the duration
of the programming time, P9.
After PGC is brought low, the programming sequence
is terminated. PGC must be held low for the time
specified by Parameter P10 to allow high-voltage
discharge of the memory array.
The code sequence to program a PIC18F2XXX/4XXX
family device is shown in Table 3-5. The flowchart,
shown in Figure 3-4, depicts the logic necessary to
completely write a PIC18F2XXX/4XXX family device.
The timing diagram that details the Start Programming
command and Parameters P9 and P10 is shown in
Figure 3-5.
TABLE 3-5: WRITE CODE MEMORY CODE SEQUENCE
Note: The TBLPTR register must point to the
same region when initiating the program-
ming sequence as it did when the write
buffers were loaded.
TABLE 3-4: WRITE AND ERASE BUFFER SIZES
Devices (Arranged by Family) Write Buffer Size (Bytes) Erase Buffer Size (Bytes)
PIC18F2221, PIC18F2321, PIC18F4221, PIC18F4321 8 64
PIC18F2450, PIC18F4450 16 64
PIC18F2410, PIC18F2510, PIC18F4410, PIC18F4510
32 64
PIC18F2420, PIC18F2520, PIC18F4420, PIC18F4520
PIC18F2423, PIC18F2523, PIC18F4423, PIC18F4523
PIC18F2480, PIC18F2580, PIC18F4480, PIC18F4580
PIC18F2455, PIC18F2550, PIC18F4455, PIC18F4550
PIC18F2458, PIC18F2553, PIC18F4458, PIC18F4553
PIC18F2515, PIC18F2610, PIC18F4515, PIC18F4610
64 64
PIC18F2525, PIC18F2620, PIC18F4525, PIC18F4620
PIC18F2585, PIC18F2680, PIC18F4585, PIC18F4680
PIC18F2682, PIC18F2685, PIC18F4682, PIC18F4685
4-Bit
Command
Data Payload Core Instruction
Step 1: Direct access to code memory and enable writes.
0000
0000
8E A6
9C A6
BSF EECON1, EEPGD
BCF EECON1, CFGS
Step 2: Load write buffer.
0000
0000
0000
0000
0000
0000
0E <Addr[21:16]>
6E F8
0E <Addr[15:8]>
6E F7
0E <Addr[7:0]>
6E F6
MOVLW <Addr[21:16]>
MOVWF TBLPTRU
MOVLW <Addr[15:8]>
MOVWF TBLPTRH
MOVLW <Addr[7:0]>
MOVWF TBLPTRL
Step 3: Repeat for all but the last two bytes.
1101 <MSB><LSB> Write 2 bytes and post-increment address by 2.
Step 4: Load write buffer for last two bytes.
1111
0000
<MSB><LSB>
00 00
Write 2 bytes and start programming.
NOP - hold PGC high for time P9 and low for time P10.
To continue writing data, repeat Steps 2 through 4, where the Address Pointer is incremented by 2 at each iteration of the loop.