M30218 Datasheet, PDF (27/179 Pages) Mitsubishi Electric Semiconductor – M30218 Group

Protection
Mitsubishi microcomputers
M30218 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
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 WA-6 shows the protect register. The values in the processor
mode register 0 (address 000416), processor mode register 1 (address 000516), system clock control reg-
ister 0 (address 000616), and system clock control register 1 (address 000716) 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 address 000A16) and processor mode
register 0 and 1 write-enable bit (bit 1 at address 000A16) 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”.
Protect register
b7 b6 b5 b4 b3 b2 b1 b0
Symbol
PRCR
Address When reset
000A16 XXXXX0002
Bit symbol
Bit name
Function
PRC0
Enables writing to system clock
control registers 0 and 1 (addresses
000616 and 000716)
0 : Write-inhibited
1 : Write-enabled
PRC1
Enables writing to processor mode
registers 0 and 1 (addresses 000416
and 000516)
0 : Write-inhibited
1 : Write-enabled
Nothing is assigned.
In an attempt to write to these bits, write “0”. The value, if read, turns out to
be indeterminate.
RW
Figure WA-6. Protect register
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