PIC18FXX20
7.1
EEADR and EEADRH
7.0
DATA EEPROM MEMORY
The address register pair can address up to a maxi-
mum of 1024 bytes of data EEPROM. The two MSbits
of the address are stored in EEADRH, while the
remaining eight LSbits are stored in EEADR. The six
Most Significant bits of EEADRH are unused, and are
read as ‘0’.
The Data EEPROM is 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 (SFR).
There are five SFRs used to read and write the
program and data EEPROM memory. These registers
are:
7.2
EECON1 and EECON2 Registers
EECON1 is the control register for EEPROM memory
accesses.
EECON2 is not a physical register. Reading EECON2
will read all ‘0’s. The EECON2 register is used
exclusively in the EEPROM write sequence.
• EECON1
• EECON2
• EEDATA
• EEADRH
• EEADR
Control bits RD and WR initiate read and write opera-
tions, respectively. These bits cannot be cleared, only
set, in software. They are cleared in hardware at the
completion of the read or write operation. The inability
to clear the WR bit in software prevents the accidental
or premature termination of a write operation.
The WREN bit, when set, will allow a write operation.
On power-up, the WREN bit is clear. The WRERR bit is
set when a write operation is interrupted by a MCLR
Reset, or a WDT Time-out Reset during normal opera-
tion. In these situations, the user can check the
WRERR bit and rewrite the location. It is necessary to
reload the data and address registers (EEDATA and
EEADR), due to the RESET condition forcing the
contents of the registers to zero.
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. EEADR and
EEADRH hold the address of the EEPROM location
being accessed. These devices have 1024 bytes of
data EEPROM with an address range from 00h to
3FFh.
The EEPROM data memory is rated for high
erase/write cycles. A byte write automatically erases
the
location
and
writes
the
new
data
(erase-before-write). 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 parameter D122 (Electrical Characteristics,
Section 26.0) for exact limits.
Note: Interrupt flag bit, EEIF in the PIR2 register,
is set when write is complete. It must be
cleared in software.
2003 Microchip Technology Inc.
Advance Information
DS39609A-page 79
MICROCHIP [ MICROCHIP ]
