PIC16F872_06 Datasheet, PDF (27/168 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS Flash Microcontroller with 10-Bit A/D

PIC16F872
3.2 Reading the EEPROM Data
Memory
Reading EEPROM Data memory only requires that the
desired address to access be written to the EEADR
register and clear the EEPGD bit. After the RD bit is set,
data will be available in the EEDATA register on the
very next instruction cycle. EEDATA will hold this value
until another read operation is initiated or until it is writ-
ten by firmware.
The steps to reading the EEPROM Data Memory are:
1. Write the address to EEDATA. Make sure that
the address is not larger than the memory size
of the device.
2. Clear the EEPGD bit to point to EEPROM Data
memory.
3. Set the RD bit to start the read operation.
4. Read the data from the EEDATA register.
EXAMPLE 3-1: EEPROM DATA READ
BSF
BCF
MOVF
MOVWF
BSF
BCF
BSF
BCF
MOVF
STATUS, RP1
STATUS, RP0
ADDR, W
EEADR
STATUS, RP0
EECON1, EEPGD
EECON1, RD
STATUS, RP0
EEDATA, W
;
;Bank 2
;Write address
;to read from
;Bank 3
;Point to Data memory
;Start read operation
;Bank 2
;W = EEDATA
3.3 Writing to the EEPROM Data
Memory
There are many steps in writing to the EEPROM Data
memory. Both address and data values must be written
to the SFRs. The EEPGD bit must be cleared and the
WREN bit must be set to enable writes. The WREN bit
should be kept clear at all times, except when writing to
the EEPROM Data. The WR bit can only be set if the
WREN bit was set in a previous operation, i.e., they
both cannot be set in the same operation. The WREN
bit should then be cleared by firmware after the write.
Clearing the WREN bit before the write actually com-
pletes will not terminate the write in progress.
Writes to EEPROM Data memory must also be pref-
aced with a special sequence of instructions that pre-
vent inadvertent write operations. This is a sequence of
five instructions that must be executed without interrup-
tion for each byte written.
The steps to write to program memory are:
1. Write the address to EEADR. Make sure that the
address is not larger than the memory size of
the device.
2. Write the 8-bit data value to be programmed in
the EEDATA registers.
3. Clear the EEPGD bit to point to EEPROM Data
memory.
4. Set the WREN bit to enable program operations.
5. Disable interrupts (if enabled).
6. Execute the special five instruction sequence:
• Write 55h to EECON2 in two steps (first to W,
then to EECON2)
• Write AAh to EECON2 in two steps (first to
W, then to EECON2)
• Set the WR bit
7. Enable interrupts (if using interrupts).
8. Clear the WREN bit to disable program operations.
9. At the completion of the write cycle, the WR bit
is cleared and the EEIF interrupt flag bit is set.
(EEIF must be cleared by firmware). Firmware
may check for EEIF to be set or WR to clear to
indicate end of program cycle.
EXAMPLE 3-2:
BSF
BCF
MOVF
MOVWF
MOVF
MOVWF
BSF
BCF
BSF
BCF
MOVLW
MOVWF
MOVLW
MOVWF
BSF
BSF
BCF
EEPROM DATA WRITE
STATUS, RP1
STATUS, RP0
ADDR, W
EEADR
VALUE, W
EEDATA
STATUS, RP0
EECON1, EEPGD
EECON1, WREN
INTCON, GIE
0x55
EECON2
0xAA
EECON2
EECON1, WR
INTCON, GIE
EECON1, WREN
;
;Bank 2
;Address to
;write to
;Data to
;write
;Bank 3
;Point to Data memory
;Enable writes
;Only disable interrupts
;if already enabled,
;otherwise discard
;Write 55h to
;EECON2
;Write AAh to
;EECON2
;Start write operation
;Only enable interrupts
;if using interrupts,
;otherwise discard
;Disable writes
© 2006 Microchip Technology Inc.
DS30221C-page 25