W79E825A Datasheet, PDF (88/127 Pages) Winbond – 8-BIT MICROCONTROLLER

W79E825A/824A/823B/822B Data Sheet
Example 5: Invalid Access
MOV
TA, #0AAh
NOP
MOV
TA, #055h
SETB
EWT
;3 M/C
;1 M/C
;3 M/C
;2 M/C
In the first three examples, the writing to the protected bits is done before the 3 machine cycles
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 is
not opened at all, and the write to the protected bit fails.
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