Mitsubishi microcomputers
M16C / 62 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Protection
49
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 1.13.6 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 reg-
ister 0 (address 0006
16
), system clock control register 1 (address 0007
16
), port P9 direction register (ad-
dress 03F3
16
) , SI/O3 control register (address 0362
16
) and SI/O4 control register (address 0366
16
) can
only be changed when the respective bit in the protect register is set to “1”. Therefore, important outputs
can be allocated to port P9.
If, after “1” (write-enabled) has been written to the port P9 direction register and SI/Oi control register
(i=3,4) write-enable bit (bit 2 at address 000A
16
), a value is written to any address, the bit automatically
reverts to “0” (write-inhibited). However, 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”.
Protect register
Symbol
PRCR
Address
000A
16
When reset
XXXXX000
2
Bit name
Bit symbol
b7
b6
b5
b4
b3
b2
b1
b0
0 : Write-inhibited
1 : Write-enabled
PRC1
PRC0
PRC2
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 0007
16
)
Enables writing to port P9 direction
register (address 03F3
16
) and SI/Oi
control register (i=3,4) (addresses
0362
16
and 0366
16
) (Note
)
0 : Write-inhibited
1 : Write-enabled
W
R
A
Nothing is assigned.
In an attempt to write to these bits, write “0”. The value, if read, turns out to be
indeterminate.
Note: Writing a value to an address 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.
A
A
A
Figure 1.13.6. Protect register