参数资料
型号: PIC18F458T-I/PT
厂商: Microchip Technology
文件页数: 78/116页
文件大小: 0K
描述: IC MCU FLASH 16KX16 W/CAN 44TQFP
产品培训模块: Asynchronous Stimulus
标准包装: 1,200
系列: PIC® 18F
核心处理器: PIC
芯体尺寸: 8-位
速度: 40MHz
连通性: CAN,I²C,SPI,UART/USART
外围设备: 欠压检测/复位,LVD,POR,PWM,WDT
输入/输出数: 33
程序存储器容量: 32KB(16K x 16)
程序存储器类型: 闪存
EEPROM 大小: 256 x 8
RAM 容量: 1.5K x 8
电压 - 电源 (Vcc/Vdd): 4.2 V ~ 5.5 V
数据转换器: A/D 8x10b
振荡器型: 外部
工作温度: -40°C ~ 85°C
封装/外壳: 44-TQFP
包装: 带卷 (TR)
PIC18FXX8
DS41159E-page 62
2006 Microchip Technology Inc.
5.5
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.
Generally, a write failure will be a bit which was written
as a ‘1’, but reads back as a ‘0’ (due to leakage off the
cell).
5.6
Protection Against Spurious Write
There are conditions when the device 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, the WREN bit is cleared.
Also, the Power-up Timer (72 ms duration) prevents
EEPROM write.
The write initiate sequence and the WREN bit together
reduce the probability of an accidental write during
brown-out, power glitch or software malfunction.
5.7
Operation During Code-Protect
Data EEPROM memory has its own code-protect
mechanism. External read and write operations are
disabled if either of these mechanisms are enabled.
The microcontroller itself can both read and write to the
internal data EEPROM, regardless of the state of the
code-protect configuration bit. Refer to Section 24.0
for
additional
information.
5.8
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).
Frequently changing values will typically be updated
more often than specification D124 or D124A. If this is
not the case, an array refresh must be performed. For
this reason, variables that change infrequently (such as
constants, IDs, calibration, etc.) should be stored in
Flash program memory. A simple data EEPROM
refresh routine is shown in Example 5-3.
EXAMPLE 5-3:
DATA EEPROM REFRESH ROUTINE
Note:
If data EEPROM is only used to store
constants and/or data that changes rarely,
an array refresh is likely not required. See
specification D124 or D124A.
CLRF
EEADR
; Start at address 0
BCF
EECON1, CFGS
; Set for memory
BCF
EECON1, EEPGD
; Set for Data EEPROM
BCF
INTCON, GIE
; Disable interrupts
BSF
EECON1, WREN
; Enable writes
Loop
; Loop to refresh array
BSF
EECON1, RD
; Read current address
MOVLW
55h
;
MOVWF
EECON2
; Write 55h
MOVLW
0AAh
;
MOVWF
EECON2
; Write AAh
BSF
EECON1, WR
; Set WR bit to begin write
BTFSC
EECON1, WR
; Wait for write to complete
BRA
$-2
INCFSZ
EEADR, F
; Increment address
BRA
Loop
; Not zero, do it again
BCF
EECON1, WREN
; Disable writes
BSF
INTCON, GIE
; Enable interrupts
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