PIC18LC658-ESLASHCL datasheet(69/366 Pages) MICROCHIP

69 / 366 page

 2000 Microchip Technology Inc.

Advanced Information

DS30475A-page 69

PIC18CXX8

5.2.2.1

Long Write Operation

The long write is what actually programs words of data

into the internal memory. When a TBLWT to the MSB of

the write block occurs, instruction execution is halted.

During this time, programming voltage and the data

stored in internal latches is applied to program memory.

For a long write to occur:

MCLR/VPP pin must be at the programming

voltage

LWRT bit must be set

TBLWT

to the address of the MSB of the write

block

If the LWRT bit is clear, a short write will occur and pro-

gram memory will not be changed. If the TBLWT is not

to the MSB of the write block, then the programming

phase is not initiated.

Setting the LWRT bit enables long writes when the

MCLR pin is taken to VPP voltage. Once the LWRT bit

is set, it can be cleared only by performing a POR or

MCLR Reset.

To ensure that the memory location has been well pro-

grammed, a minimum programming time is required.

The long write can be terminated after the program-

ming time has expired by a RESET or an interrupt.

Having only one interrupt source enabled to terminate

the long write, ensures that no unintended interrupts

will prematurely terminate the long write.

5.2.2.2

Sequence of Events

The sequence of events for programming an internal

program memory location should be:

Enable the interrupt that terminates the long

write. Disable all other interrupts.

Clear the source interrupt flag.

If Interrupt Service Routine execution is desired

when

the

device

wakes,

enable

global

interrupts.

Set LWRT bit in the RCON register.

Raise MCLR/VPP pin to the programming

voltage, VPP.

Clear the WDT (if enabled).

Set the interrupt source to interrupt at the

required time.

Execute the Table Write for the lower (even)

byte. This will be a short write.

Execute the Table Write for the upper (odd) byte.

This will be a long write. The controller will HALT

while programming. The interrupt wakes the

controller.

10. If GIE was set, service the interrupt request.

11. Go to 7 if more bytes to be programmed.

12. Lower MCLR/VPP pin to VDD.

13. Verify the memory location (table read).

14. Reset the device.

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