Mitsubishi microcomputers
M16C / 61 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
Protection
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 1.12.6 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), system clock control register 1 (address 000716) and port P9 direction register
(address 03F316) can only be changed when the respective bit in the protect register is set to “1”. There-
fore, important outputs can be allocated to port P9.
If, after “1” (write-enabled) has been written to the port P9 direction register write-enable bit (bit 2 at address
000A16), 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 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
000A16
When reset
XXXXX0002
Bit symbol
PRC0
Bit name
Function
0 : Write-inhibited
R W
Enables writing to system clock
control registers 0 and 1 (addresses
1 : Write-enabled
000616 and 000716
)
Enables writing to processor mode
registers 0 and 1 (addresses 000416
0 : Write-inhibited
1 : Write-enabled
PRC1
PRC2
and 000516
)
Enables writing to port P9 direction
register (address 03F316) (Note)
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.
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.
Figure 1.12.6. Protect register
39
MITSUBISHI [ Mitsubishi Group ]
