M30222 Datasheet, PDF (34/237 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

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MITSUBISHI MICROCOMPUTERS
Specifications in this manual are tentative and subject to change
M30222 Group
Rev. G
Protection
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 1.20 shows the protect register. The values in the processor
mode register 0 (address 000416), processor mode register 1 (address 000516), system clock control
register 0 (address 000616), system clock control register 1 (address 000716), Port P9 direction register
(address 03F316) and VDC control register (address 001816)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 000A16) and processor mode register
0 and 1 write-enable bit (bit 1 at 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 XXXX0000 2
Bit symbol
PRC0
Bit name
Enables writing to system clock
control registers 0 and 1 (addresses
000616 and 000716)
Function
0 : Write-inhibited
1 : Write-enabled
PRC1
Enables writing to processor mode
registers 0 and 1 (addresses 0004 16 ^{0 : Write-inhibited}
and 000516)
1 : Write-enabled
PRC2
Enables writing to Port P9 direction
register (address 03F3 16) and SI/Oi
control register (i=3,4) (addresses
036216 and 036616) (Note)
0 : Write-inhibited
1 : Write-enabled
PRC3
Enables writing to VDC control
register (address 001816)
0 : Write-inhibited
1 : Write-enabled
RW
OO
Nothing is assigned.
Write "0" when writing to these bits. If read, the value is indeterminate.
Note: Writing a value to these addresses after “1” is written to this bit returns the bit
to “0” . Other bits do not automatically return to “0” and they must
therefore be reset by the program
Fig. 1.20. Protect register
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