DS80C320 Datasheet, PDF (18/42 Pages) Dallas Semiconductor – High-Speed/Low-Power Micro

DS80C320/DS80C323
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 Band-gap Select
POR Power-on Reset flag
EWT Enable Watchdog
RWT Reset Watchdog
WDIF Watchdog Interrupt Flag
SPECIAL FUNCTION REGISTERS
Most special features of the DS80C320/DS80C323 or 80C32 are controlled by bits in special function
registers (SFRs). This allows the device to add many features but use the same instruction set. When
writing software to use a new feature, the SFR must be defined to an assembler or compiler using an
equate statement. This is the only change needed to access the new function. The DS80C320/DS80C323
duplicates the SFRs that are contained in the standard 80C32. Table 6 shows the register addresses and bit
locations. Many are standard 80C32 registers. The High-Speed Microcontroller User’s Guide describes
all SFRs.
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