PIC16F1516 datasheet(97/344 Pages) MICROCHIP

97 / 344 page

 2011 Microchip Technology Inc.

Preliminary

DS41452B-page 97

PIC16(L)F1516/7/8/9

11.0

FLASH PROGRAM MEMORY

CONTROL

The Flash program memory is readable and writable

during normal operation over the full VDD range.

Program memory is indirectly addressed using Special

Function Registers (SFRs). The SFRs used to access

program memory are:

•PMCON1

•PMCON2

•PMDATL

•PMDATH

• PMADRL

•PMADRH

When

accessing

the

program

memory,

the

PMDATH:PMDATL register pair forms a 2-byte word

that holds the 14-bit data for read/write, and the

PMDATH:PMDATL register pair forms a 2-byte word

that holds the 15-bit address of the program memory

location being read.

The write time is controlled by an on-chip timer. The write/

erase voltages are generated by an on-chip charge pump

rated to operate over the operating voltage range of the

device.

The Flash program memory can be protected in two

ways; by code protection (CP bit in Configuration Word 1)

and write protection (WRT<1:0> bits in Configuration

Word 2).

Code protection (CP = 0)(1), disables access, reading

and writing, to the Flash program memory via external

device programmers. Code protection does not affect

the self-write and erase functionality. Code protection

can only be reset by a device programmer performing

a Bulk Erase to the device, clearing all Flash program

memory, Configuration bits and User IDs.

Write protection prohibits self-write and erase to a

portion or all of the Flash program memory as defined

by the bits WRT<1:0>. Write protection does not affect

a device programmers ability to read, write or erase the

device.

11.1

PMADRL and PMADRH Registers

The PMADRH:PMADRL register pair can address up

to a maximum of 32K words of program memory. When

selecting a program address value, the MSB of the

address is written to the PMADRH register and the LSB

is written to the PMADRL register.

11.1.1

PMCON1 AND PMCON2

REGISTERS

PMCON1 is the control register for Flash program

memory accesses.

Control bits RD and WR initiate read and write,

respectively. These bits cannot be cleared, only set, in

software. They are cleared by hardware at completion

of the read or write operation. The inability to clear the

WR bit in software prevents the accidental, premature

termination of a write operation.

The WREN bit, when set, will allow a write operation to

occur. On power-up, the WREN bit is clear. The

WRERR bit is set when a write operation is interrupted

by a Reset during normal operation. In these situations,

following Reset, the user can check the WRERR bit

and execute the appropriate error handling routine.

The PMCON2 register is a write-only register. Attempting

to read the PMCON2 register will return all ‘0’s.

To enable writes to the program memory, a specific

pattern (the unlock sequence), must be written to the

PMCON2 register. The required unlock sequence

prevents inadvertent writes to the program memory

write latches and Flash program memory.

11.2

Flash Program Memory Overview

It is important to understand the Flash program memory

structure for erase and programming operations. Flash

program memory is arranged in rows. A row consists of

a fixed number of 14-bit program memory words. A row

is the minimum size that can be erased by user software.

After a row has been erased, the user can reprogram

all or a portion of this row. Data to be written into the

program memory row is written to 14-bit wide data write

latches. These write latches are not directly accessible

to the user, but may be loaded via sequential writes to

the PMDATH:PMDATL register pair.

See Table 11-1 for Erase Row size and the number of

write latches for Flash program memory.

Note 1:

Code protection of the entire Flash

program memory array is enabled by

clearing the CP bit of Configuration Word 1.

Note:

If the user wants to modify only a portion

of a previously programmed row, then the

contents of the entire row must be read

and saved in RAM prior to the erase.

Then, new data and retained data can be

written into the write latches to reprogram

the row of Flash program memory. How-

ever, any unprogrammed locations can be

written without first erasing the row. In this

case, it is not necessary to save and

rewrite the other previously programmed

locations.

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