PIC18F8722IPTSQTP datasheet(95/446 Pages) MICROCHIP

95 / 446 page

DS39646C-page 93

PIC18F8722 FAMILY

6.5

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.

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 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 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.

FIGURE 6-5:

TABLE WRITES TO FLASH PROGRAM MEMORY

6.5.1

FLASH PROGRAM MEMORY WRITE

SEQUENCE

The sequence of events for programming an internal

program memory location should be:

Read 64 bytes into RAM.

Update data values in RAM as necessary.

Load Table Pointer register with address being

erased.

Execute the row erase procedure.

Load Table Pointer register with address of first

byte being written.

Write the 64 bytes into the holding registers with

auto-increment.

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 to enable byte writes.

Disable interrupts.

Write 55h to EECON2.

10. Write 0AAh to EECON2.

11. Set the WR bit. This will begin the write cycle.

12. The CPU will stall for duration of the write for TIW

(see parameter D133A).

13. Re-enable interrupts.

14. Verify the memory (table read).

An example of the required code is shown in

Example 6-3 on the following page.

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 holding registers

before executing a write operation.

TABLAT

TBLPTR = xxxx3F

TBLPTR = xxxxx1

TBLPTR = xxxxx0

Write Register

TBLPTR = xxxxx2

Program Memory

Holding Register

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.

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