Rainbow Electronics W79E8213R - Manual (Page 69)

Preliminary W79E8213/W79E8213R Data Sheet
Publication Release Date: July 11, 2008
- 69 - Revision A2
Example 5: Invalid Access
MOV TA, #0AAh ; 3 M/C
NOP ; 1 M/C
MOV TA, #055h ; 3 M/C
SETB EWT ; 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.