W79E548 Datasheet, PDF (61/79 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E548/W79L548
Examples of Timed Assessing are shown below.
Example 1: Valid access
MOV
MOV
MOV
TA, #0AAh 3 M/C
TA, #055h 3 M/C
WDCON, #00h 3 M/C
Example 2: Valid access
MOV
MOV
NOP
SETB
TA, #0AAh
TA, #055h
EWT
3 M/C
3 M/C
1 M/C
2 M/C
Example 3: Valid access
MOV
MOV
ORL
TA, #0Aah 3 M/C
TA, #055h 3 M/C
WDCON, #00000010B 3M/C
Example 4: Invalid access
MOV
MOV
NOP
NOP
CLR
TA, #0AAh
TA, #055h
POR
3 M/C
3 M/C
1 M/C
1 M/C
2 M/C
Example 5: Invalid Access
MOV
NOP
MOV
SETB
TA, #0AAh
TA, #055h
EWT
3 M/C
1 M/C
3 M/C
2 M/C
Note: M/C = Machine Cycles
In the first three examples, the writing to the protected bits is done before the 3 machine cycle window
closes. In Example 4, however, the writing to the protected bit occurs after the window has closed,
and so there is effectively no change in the status of the protected bit. In Example 5, the second write
to TA occurs 4 machine cycles after the first write, therefore the timed access window in not opened at
all, and the write to the protected bit fails.
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Publication Release Date: December 12, 2005
Revision A1