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Chapter 3
CPU System Functions
Preliminary User’s Manual U17566EE1V2UM00
3.6 Write Protected Registers
Write protected registers are protected from inadvertent write access due to
erroneous program execution, etc. Write access to a write protected register is
only given immediately after writing to a corresponding write enable register.
For a write access to the write protected registers you have to use the following
instructions:
1. Store instruction (ST/SST instruction)
2. Bit operation instruction (SET1/CLR1/NOT1 instruction)
When
reading
write protected registers, no special sequence is required.
The following table gives an overview of the write protected registers and their
corresponding write enable registers.
For some registers, incorrect store operations can be checked by a flag of the
corresponding status register. This is also marked in the table below.
Table 3-15
Overview of write protected registers
Write protected register
Shortcut
Corresponding write
enable register
Shortcut
Status
register
For details see
Clock control register
CKC
Peripheral command
register
PHCMD
PHS
“Clock Generator“
on page 129
Watchdog timer clock
control register
WCC
Processor clock control
register
PCC
Watch Timer clock control
register
TCC
SPCLK control register
SCC
FOUTCLK control register
FCC
I
2
C clock control register
ICC
Main oscillator clock
monitor mode register
CLMM
Main oscillator clock
monitor command
protection register
PRCMDCMM
––
“Clock Generator“
on page 129
Sub oscillator clock monitor
mode register
CLMS
Sub oscillator clock
monitor command
protection register
PRCMDCMS
Power save control register
PSC
Command register
PRCMD
–
“Clock Generator“
on page 129
Self-programming enable
control register
a
a)
Flash memory devices only
SELFEN
Sequence protect
register
SELFENP
–
“Flash Memory“
on page 229
Watchdog timer frequency
select register
WDCS
Watchdog timer
security register
WCMD
WPHS
“Watchdog Timer
(WDT)“ on
page 497
Watchdog timer mode
register
WDTM
N-Wire security disable
control register
RSUDISC
RSUDISC write
protection register
RSUDISCP
–
“On-Chip Debug
Unit“ on page 877
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