PIC16F87X datasheet(41/200 Pages) MICROCHIP

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PIC16F87X

Preliminary

DS30292A-page 41

4.0

DATA EEPROM AND FLASH

PROGRAM MEMORY

The Data EEPROM and FLASH Program memory are

readable and writable during normal operation over the

entire VDD range. The data memory is not directly

mapped in the register ﬁle space. Instead it is indirectly

addressed through the Special Function Registers.

There are six SFRs used to read and write the program

and data EEPROM memory. These registers are:

• EECON1

• EECON2

• EEDATA

• EEDATH

• EEADR

• EEADRH

The EEPROM data memory allows byte read and write.

When interfacing to the data memory block, EEDATA

holds the 8-bit data for read/write, and EEADR holds

the address of the EEPROM location being accessed.

The registers EEDATH and EEADRH are not used for

data EEPROM access. These devices have up to 256

bytes of data EEPROM with an address range from 0h

to FFh.

The EEPROM data memory is rated for high erase/

write cycles. The write time is controlled by an on-chip

timer. The write time will vary with voltage and temper-

ature as well as from chip to chip. Please refer to the

speciﬁcations for exact limits.

The program memory allows word reads and writes.

Program memory reads allow checksum calculation for

UL type applications. A byte or word write automatically

erases the location and writes the new data (erase

before write).

When interfacing to the program memory block, the

EEDATH:EEDATA registers form a 2 byte word which

holds

the

14-bit

data

for

read/write,

and

the

EEADRH:EEADR registers form a 2 byte word which

holds the 13-bit address of the EEPROM location being

accessed. These devices can have up to 8K words of

program EEPROM with an address range from 0h to

3FFFh.

The value written to program memory does not need to

be a valid instruction. Therefore, up to 14-bit numbers

can be stored in memory for use as calibration param-

eters, serial numbers, packed 7-bit ASCII, etc. Execut-

ing a program memory location containing data that

forms an invalid instruction results in a NOP.

4.1

EEADR

The address registers can address up to a maximum of

256 bytes of data EEPROM or up to a maximum of 8K

words of program FLASH.

When selecting a program address value, the MSByte

of the address is written to the EEADRH register and

the LSByte is written to the EEADR register. When

selecting a data address value, only the LSByte of the

address is written to the EEADR register.

On the PIC16F874/873 devices with 128 bytes of

EEPROM, the MSbit of the EEADR must always be

cleared to prevent inadvertent access to the wrong

location. This also applies to the program memory. The

upper MSbits of EEADRH must always be clear.

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