PIC16F1516 datasheet(103/344 Pages) MICROCHIP

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Preliminary

DS41452B-page 103

PIC16(L)F1516/7/8/9

11.2.4

WRITING TO FLASH PROGRAM

MEMORY

Program memory is programmed using the following

steps:

Load the address in PMADRH:PMADRL of the

row to be programmed.

Load each write latch with data.

Initiate a programming operation.

Repeat steps 1 through 3 until all data is written.

Before writing to program memory, the word(s) to be

written must be erased or previously unwritten. Pro-

gram memory can only be erased one row at a time. No

automatic erase occurs upon the initiation of the write.

Program memory can be written one or more words at

a time. The maximum number of words written at one

time is equal to the number of write latches. See

Figure 11-5 (row writes to program memory with 32

write latches) for more details.

The write latches are aligned to the Flash row address

boundary

defined

the

upper

10-bits

PMADRH:PMADRL, (PMADRH<6:0>:PMADRL<7:5>)

with the lower 5-bits of PMADRL, (PMADRL<4:0>)

determining the write latch being loaded. Write opera-

tions do not cross these boundaries. At the completion

of a program memory write operation, the data in the

write latches is reset to contain 0x3FFF.

The following steps should be completed to load the

write latches and program a row of program memory.

These steps are divided into two parts. First, each write

latch is loaded with data from the PMDATH:PMDATL

using the unlock sequence with LWLO = 1. When the

last word to be loaded into the write latch is ready, the

LWLO bit is cleared and the unlock sequence

executed. This initiates the programming operation,

writing all the latches into Flash program memory.

Set the WREN bit of the PMCON1 register.

Clear the CFGS bit of the PMCON1 register.

Set the LWLO bit of the PMCON1 register.

When the LWLO bit of the PMCON1 register is

‘1’, the write sequence will only load the write

latches and will not initiate the write to Flash

program memory.

Load the PMADRH:PMADRL register pair with

the address of the location to be written.

Load the PMDATH:PMDATL register pair with

the program memory data to be written.

Execute the unlock sequence (Section 11.2.2

“Flash Memory Unlock Sequence”

). The write

latch is now loaded.

Increment the PMADRH:PMADRL register pair

to point to the next location.

Repeat steps 5 through 7 until all but the last

write latch has been loaded.

Clear the LWLO bit of the PMCON1 register.

When the LWLO bit of the PMCON1 register is

‘0’, the write sequence will initiate the write to

Flash program memory.

10. Load the PMDATH:PMDATL register pair with

the program memory data to be written.

11. Execute the unlock sequence (Section 11.2.2

“Flash Memory Unlock Sequence”

). The

entire program memory latch content is now

written to Flash program memory.

An example of the complete write sequence is shown in

Example 11-3. The initial address is loaded into the

PMADRH:PMADRL register pair; the data is loaded

using indirect addressing.

Note:

The special unlock sequence is required

to load a write latch with data or initiate a

Flash programming operation. If the

unlock sequence is interrupted, writing to

the latches or program memory will not be

initiated.

Note:

The program memory write latches are

reset to the blank state (0x3FFF) at the

completion of every write or erase

operation. As a result, it is not necessary

to load all the program memory write

latches. Unloaded latches will remain in

the blank state.

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