PIC16F84A datasheet(33/124 Pages) MICROCHIP

33 / 124 page

PIC16F8X

DS30430C-page 33

7.0

DATA EEPROM MEMORY

The EEPROM data memory is readable and writable

during normal operation (full VDD range). This memory

is not directly mapped in the register ﬁle space. Instead

it is indirectly addressed through the Special Function

Registers. There are four SFRs used to read and write

this memory. These registers are:

• EECON1

• EECON2

• EEDATA

• EEADR

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

holds the address of the EEPROM location being

accessed. PIC16F8X devices have 64 bytes of data

EEPROM with an address range from 0h to 3Fh.

The EEPROM data memory allows byte read and write.

A byte write automatically erases the location and

writes the new data (erase before write). 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 temperature as well as

from chip to chip. Please refer to AC speciﬁcations for

exact limits.

When the device is code protected, the CPU may

continue to read and write the data EEPROM memory.

The device programmer can no longer access

this memory.

7.1

EEADR

The EEADR register can address up to a maximum of

256 bytes of data EEPROM. Only the ﬁrst 64 bytes of

data EEPROM are implemented.

The upper two bits are address decoded. This means

that these two bits must always be '0' to ensure that the

address is in the 64 byte memory space.

FIGURE 7-1:

EECON1 REGISTER (ADDRESS 88h)

R/W-0

R/W-x

R/W-0

R/S-0

R/S-x

—

EEIF

WRERR

WREN

= Readable bit

W = Writable bit

= Settable bit

= Unimplemented bit,

read as ‘0’

- n = Value at POR reset

bit7

bit0

bit 7:5

Unimplemented: Read as '0'

bit 4

EEIF: EEPROM Write Operation Interrupt Flag bit

1 = The write operation completed (must be cleared in software)

0 = The write operation is not complete or has not been started

bit 3

WRERR: EEPROM Error Flag bit

1 = A write operation is prematurely terminated

(any MCLR reset or any WDT reset during normal operation)

0 = The write operation completed

bit 2

WREN: EEPROM Write Enable bit

1 = Allows write cycles

0 = Inhibits write to the data EEPROM

bit 1

WR: Write Control bit

1 = initiates a write cycle. (The bit is cleared by hardware once write is complete. The WR bit can only

be set (not cleared) in software.

0 = Write cycle to the data EEPROM is complete

bit 0

RD: Read Control bit

1 = Initiates an EEPROM read (read takes one cycle. RD is cleared in hardware. The RD bit can only

be set (not cleared) in software).

0 = Does not initiate an EEPROM read

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