PIC18F2331/2431/4331/4431
7.0
DATA EEPROM MEMORY
7.2
EECON1 and EECON2 Registers
The data EEPROM is readable and writable during
normal operation over the entire V
DD
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 four SFRs used to read and write the
program and data EEPROM memory. These registers
are:
•
•
•
•
EECON1
EECON2
EEDATA
EEADR
Access to the data EEPROM is controlled by two
registers: EECON1 and EECON2. These are the same
registers which control access to the program memory
and are used in a similar manner for the data
EEPROM.
The EECON1 register (Register
is the control
register for data and program memory access. Control
bit, EEPGD, determines if the access will be to program
or data EEPROM memory. When clear, operations will
access the data EEPROM memory. When set, program
memory is accessed.
Control bit, CFGS, determines if the access will be to
the Configuration registers or to program memory/data
EEPROM memory. When set, subsequent operations
access Configuration registers. When CFGS is clear,
the EEPGD bit selects either Flash program or data
EEPROM memory.
The WREN bit, when set, will allow a write operation.
On power-up, the WREN bit is clear. The WRERR bit is
set in hardware when the WREN bit is set and cleared
when the internal programming timer expires and the
write operation is complete.
Note:
During normal operation, the WRERR bit
is read as ‘1’. This can indicate that a write
operation was prematurely terminated by
a Reset or a write operation was
attempted improperly.
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.
These devices have 256 bytes of data EEPROM with
an address range from 00h to FFh.
The EEPROM data memory is rated for high erase/
write cycle endurance. 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
in
for exact limits.
7.1
EEADR
The Address register can address 256 bytes of data
EEPROM.
The WR control bit initiates write operations. The bit
cannot be cleared, only set, in software; it is cleared in
hardware at the completion of the write operation.
Note:
The EEIF interrupt flag bit (PIR2<4>) is
set when the write is complete. It must be
cleared in software.
Control bits, RD and WR, start read and erase/write
operations, respectively. These bits are set by firmware
and cleared by hardware at the completion of the
operation.
The RD bit cannot be set when accessing program
memory (EEPGD =
1).
Program memory is read using
table read instructions. See
regarding table reads.
The EECON2 register is not a physical register. It is
used exclusively in the memory write and erase
sequences. Reading EECON2 will read all ‘0’s.
2010 Microchip Technology Inc.
DS39616D-page 79
MICROCHIP [ MICROCHIP TECHNOLOGY ]
