PIC16F1847_13 Datasheet, PDF (104/440 Pages) Microchip Technology – 18/20/28-Pin Flash Microcontrollers with XLP Technology

PIC16(L)F1847
11.2 Using the Data EEPROM
The data EEPROM is a high-endurance, byte address-
able array that has been optimized for the storage of
frequently changing information (e.g., program
variables or other data that are updated often). When
variables in one section change frequently, while
variables in another section do not change, it is
possible to exceed the total number of write cycles to
the EEPROM without exceeding the total number of
write cycles to a single byte. Refer to Section 30.0
“Electrical Specifications”. If this is the case, then a
refresh of the array must be performed. For this reason,
variables that change infrequently (such as constants,
IDs, calibration, etc.) should be stored in Flash program
memory.
11.2.1 READING THE DATA EEPROM
MEMORY
To read a data memory location, the user must write
the address to the EEADRL register, clear the EEPGD
and CFGS control bits of the EECON1 register, and
then set control bit RD. The data is available at the very
next cycle, in the EEDATL register; therefore, it can be
read in the next instruction. EEDATL will hold this value
until another read or until it is written to by the user
(during a write operation).
EXAMPLE 11-1: DATA EEPROM READ
BANKSEL EEADRL
;
MOVLW DATA_EE_ADDR ;
MOVWF EEADRL
;Data Memory
;Address to read
BCF
EECON1, CFGS ;Deselect Config space
BCF
EECON1, EEPGD;Point to DATA memory
BSF
EECON1, RD ;EE Read
MOVF EEDATL, W ;W = EEDATL
Note: Data EEPROM can be read regardless of
the setting of the CPD bit.
11.2.2 WRITING TO THE DATA EEPROM
MEMORY
To write an EEPROM data location, the user must first
write the address to the EEADRL register and the data
to the EEDATL register. Then the user must follow a
specific sequence to initiate the write for each byte.
The write will not initiate if the above sequence is not
followed exactly (write 55h to EECON2, write AAh to
EECON2, then set WR bit) for each byte. Interrupts
should be disabled during this code segment.
Additionally, the WREN bit in EECON1 must be set to
enable write. This mechanism prevents accidental
writes to data EEPROM due to errant (unexpected)
code execution (i.e., lost programs). The user should
keep the WREN bit clear at all times, except when
updating EEPROM. The WREN bit is not cleared
by hardware.
After a write sequence has been initiated, clearing the
WREN bit will not affect this write cycle. The WR bit will
be inhibited from being set unless the WREN bit is set.
At the completion of the write cycle, the WR bit is
cleared in hardware and the EE Write Complete
Interrupt Flag bit (EEIF) is set. The user can either
enable this interrupt or poll this bit. EEIF must be
cleared by software.
11.2.3 PROTECTION AGAINST SPURIOUS
WRITE
There are conditions when the user may not want to
write to the data EEPROM memory. To protect against
spurious EEPROM writes, various mechanisms have
been built-in. On power-up, WREN is cleared. Also, the
Power-up Timer (64 ms duration) prevents EEPROM
write.
The write initiate sequence and the WREN bit together
help prevent an accidental write during:
• Brown-out
• Power Glitch
• Software Malfunction
11.2.4 DATA EEPROM OPERATION
DURING CODE-PROTECT
Data memory can be code-protected by programming
the CPD bit in the Configuration Words to ‘0’.
When the data memory is code-protected, only the
CPU is able to read and write data to the data
EEPROM. It is recommended to code-protect the
program memory when code-protecting data memory.
This prevents anyone from replacing your program with
a program that will access the contents of the data
EEPROM.
DS40001453D-page 104
Preliminary
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