Protection
M30240 Group
Rev.1.00 Sep 24, 2003 Page 27 of 360
1.2.11 Protection
The protection function is provided so that the values in important registers cannot be changed in the
event that the program runs out of control. Figure 1.14 shows the protect register. The values in the
processor mode register 0 (address 0004
16
), processor mode register 1 (address 0005
16
), system clock
control register 0 (address 0006
16
), system clock control register 1 (address 0007
16
) and frequency
synthesizer registers can only be changed when the respective bit in the protect register is set to “1”.
The system clock control registers 0 and 1 write-enable bit (bit 0 at 000A
16
) and processor mode register
0 and 1 write-enable bit (bit 1 at 000A
16
) do not automatically return to “0” after a value has been written
to an address. The program must therefore be written to return these bits to “0”.
Figure 1.14: Protect register
Protect register
Symbol Address When reset
PRCR 000A
16 XXXXX0002
Bit nameBit symbol
b7 b6 b5 b4 b3 b2 b1 b0
0 : Write-inhibited
1 : Write-enabled
PRC1
PRC0
Enables writing to processor mode
registers 0 and 1 (addresses 0004
16
and 0005
16)
Function
0 : Write-inhibited
1 : Write-enabled
Enables writing to system clock
control registers 0 and 1 (addresses
0006
16 and 000716
) and frequency
synthesizer registers (addresses
03DB16 to 03DF16
)
WR
Nothing is assigned.
These bits can neither be set nor reset. When read, their contents are
indeterminate.
Reserved bit
Must always be set to "0"
O
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