Microchip Technology MA160014 データシート
2010-2012 Microchip Technology Inc.
DS41412F-page 107
PIC18(L)F2X/4XK22
7.3
Reading the Data EEPROM
Memory
Memory
To read a data memory location, the user must write
the address to the EEADR register, clear the EEPGD
control bit of the EECON1 register and then set control
bit, RD. The data is available on the very next instruc-
tion cycle; therefore, the EEDATA register can be read
by the next instruction. EEDATA will hold this value until
another read operation, or until it is written to by the
user (during a write operation).
the address to the EEADR register, clear the EEPGD
control bit of the EECON1 register and then set control
bit, RD. The data is available on the very next instruc-
tion cycle; therefore, the EEDATA register can be read
by the next instruction. EEDATA will hold this value until
another read operation, or until it is written to by the
user (during a write operation).
The basic process is shown in
.
7.4
Writing to the Data EEPROM
Memory
Memory
To write an EEPROM data location, the address must
first be written to the EEADR register and the data writ-
ten to the EEDATA register. The sequence in
first be written to the EEADR register and the data writ-
ten to the EEDATA register. The sequence in
must be followed to initiate the write cycle.
The write will not begin if this sequence is not exactly
followed (write 55h to EECON2, write 0AAh to
EECON2, then set WR bit) for each byte. It is strongly
recommended that interrupts be disabled during this
code segment.
followed (write 55h to EECON2, write 0AAh to
EECON2, then set WR bit) for each byte. It is strongly
recommended that interrupts be disabled during this
code segment.
Additionally, the WREN bit in EECON1 must be set to
enable writes. This mechanism prevents accidental
writes to data EEPROM due to unexpected code
execution (i.e., runaway programs). The WREN bit
should be kept clear at all times, except when updating
the EEPROM. The WREN bit is not cleared by
hardware.
enable writes. This mechanism prevents accidental
writes to data EEPROM due to unexpected code
execution (i.e., runaway programs). The WREN bit
should be kept clear at all times, except when updating
the EEPROM. The WREN bit is not cleared by
hardware.
After a write sequence has been initiated, EECON1,
EEADR and EEDATA cannot be modified. The WR bit
will be inhibited from being set unless the WREN bit is
set. Both WR and WREN cannot be set with the same
instruction.
EEADR and EEDATA cannot be modified. The WR bit
will be inhibited from being set unless the WREN bit is
set. Both WR and WREN cannot be set with the same
instruction.
At the completion of the write cycle, the WR bit is
cleared by hardware and the EEPROM Interrupt Flag
bit, EEIF, is set. The user may either enable this
interrupt or poll this bit. EEIF must be cleared by
software.
cleared by hardware and the EEPROM Interrupt Flag
bit, EEIF, is set. The user may either enable this
interrupt or poll this bit. EEIF must be cleared by
software.
7.5
Write Verify
Depending on the application, good programming
practice may dictate that the value written to the
memory should be verified against the original value.
This should be used in applications where excessive
writes can stress bits near the specification limit.
practice may dictate that the value written to the
memory should be verified against the original value.
This should be used in applications where excessive
writes can stress bits near the specification limit.
EXAMPLE 7-1:
DATA EEPROM READ
EXAMPLE 7-2:
DATA EEPROM WRITE
MOVLW
DATA_EE_ADDR
;
MOVWF
EEADR
; Data Memory Address to read
BCF
EECON1, EEPGD
; Point to DATA memory
BCF
EECON1, CFGS
; Access EEPROM
BSF
EECON1, RD
; EEPROM Read
MOVF
EEDATA, W
; W = EEDATA
MOVLW
DATA_EE_ADDR_LOW
;
MOVWF
EEADR
; Data Memory Address to write
MOVLW
DATA_EE_ADDR_HI
;
MOVWF
EEADRH
;
MOVLW
DATA_EE_DATA
;
MOVWF
EEDATA
; Data Memory Value to write
BCF
EECON1, EEPGD
; Point to DATA memory
BCF
EECON1, CFGS
; Access EEPROM
BSF
EECON1, WREN
; Enable writes
BCF
INTCON, GIE
; Disable Interrupts
MOVLW
55h
;
Required
MOVWF
EECON2
; Write 55h
Sequence
MOVLW
0AAh
;
MOVWF
EECON2
; Write 0AAh
BSF
EECON1, WR
; Set WR bit to begin write
BSF
INTCON, GIE
; Enable Interrupts
; User code execution
BCF
EECON1, WREN
; Disable writes on write complete (EEIF set)