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參數資料
型號： W79E201A16PN
廠商： WINBOND ELECTRONICS CORP
元件分類： 微控制器/微處理器
英文描述： 8-BIT MICROCONTROLLER
中文描述： 8-BIT, FLASH, 16 MHz, MICROCONTROLLER, PQCC44
封裝： ROHS COMPLIANT, PLASTIC, LCC-44
文件頁數： 63/87頁
文件大小： 818K
代理商： W79E201A16PN
W79E201
Publication Release Date: December 16, 2004
- 63 -
Revision A2
16. TIMED ACCESS PROTECTION
The W79E201 has several new features, like the Watchdog timer, on-chip ROM size adjustment, wait
state control signal and Power on/fail reset flag, which are crucial to proper operation of the system. If
left unprotected, errant code may write to the Watchdog control bits resulting in incorrect operation
and loss of control. In order to prevent this, the W79E201 has a protection scheme which controls the
write access to critical bits. This protection scheme is done using a timed access.
In this method, the bits which are to be protected have a timed write enable window. A write is
successful only if this window is active, otherwise the write will be discarded. This write enable window
is open for 3 machine cycles if certain conditions are met. After 3 machine cycles, this window
automatically closes. The window is opened by writing AAh and immediately 55h to the Timed Access
(TA) SFR. This SFR is located at address C7h. The suggested code for opening the timed access
window is
TA
REG
0C7h
; Define new register TA, located at 0C7h
MOV
TA, #0AAh
MOV
TA, #055h
When the software writes AAh to the TA SFR, a counter is started. This counter waits for 3 machine
cycles looking for a write of 55h to TA. If the second write (55h) occurs within 3 machine cycles of the
first write (AAh), then the timed access window is opened. It remains open for 3 machine cycles,
during which the user may write to the protected bits. Once the window closes the procedure must be
repeated to access the other protected bits.
Examples of Timed Assessing are shown below.
Example 1: Valid access
MOV
TA, #0AAh
3 M/C ; Note: M/C = Machine Cycles
MOV
TA, #055h
3 M/C
MOV
WDCON, #00h
3 M/C
Example 2: Valid access
MOV
TA, #0AAh
3 M/C
MOV
TA, #055h
3 M/C
NOP
1 M/C
SETB EWT
2 M/C
Example 3: Valid access
MOV
TA, #0Aah
3 M/C
MOV
TA, #055h
3 M/C
ORL
WDCON, #00000010B 3M/C
Example 4: Invalid access
MOV
TA, #0AAh
3 M/C
MOV
TA, #055h
3 M/C
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相關代理商/技術參數
參數描述
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W79E2051RARG 制造商:Nuvoton Technology Corp 功能描述:IC MCU 2KB FLASH 20SSOP
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