W79E225A_08 Datasheet, PDF (178/203 Pages) Winbond – 8-bit Microcontroller

Preliminary W79E225A/226A/227A 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 protected bits are written before the window closes. In Example 4,
however, the write occurs after the window has closed, so there is no change in the protected bit. In
Example 5, the second write to TA occurs four machine cycles after the first write, so the timed access
window in not opened at all, and the write to the protected bit fails.
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Publication Release Date: April 15, 2008
Revision A4.0