DS80C320_06 Datasheet, PDF (19/40 Pages) Maxim Integrated Products – High-Speed/Low-Power Microcontrollers

DS80C320/DS80C323 High-Speed/Low-Power Microcontrollers
Figure 4. Ring Oscillator Startup
DIAGRAM ASSUMES THAT THE OPERATION FOLLOWING STOP REQUIRES LESS THAN 18ms COMPLETE.
TIMED ACCESS PROTECTION
Selected SFR bits are critical to operation, making it desirable to protect against an accidental write
operation. The Timed Access procedure prevents an errant CPU from accidentally altering a bit that
would cause difficulty. The Timed Access procedure requires that the write of a protected bit be preceded
by the following instructions:
MOV
MOV
0C7h, #0AAh
0C7h, #55h
By writing an AAh followed by a 55h to the Timed Access register (location C7h), the hardware opens a
three-cycle window that allows software to modify one of the protected bits. If the instruction that seeks
to modify the protected bit is not immediately proceeded by these instructions, the write will not take
effect. The protected bits are:
EXIF.0
WDCON.6
WDCON.1
WDCON.0
WDCON.3
BGS Bandgap Select
POR Power-on Reset flag
EWT Enable Watchdog
RWT Reset Watchdog
WDIF Watchdog Interrupt Flag
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