M16C1N Datasheet, PDF (52/238 Pages) Renesas Technology Corp – RENESAS 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/10 SERIES

M16C/1N Group
7. Protection
7. 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 7.1 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 P0 direction register
(address 00E216) 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 P0.
If, after "1" (write-enabled) has been written to bit "enables writing to port P0 direction register" (bit 2 at
address 000A16), a value is written to any address, the bit automatically reverts to "0" (write-inhibited).
Make sure no interrupts will generate between the instruction in which the PRC2 bit to "1" and the next
instruction. The system clock control registers 0 and 1 and oscillation stop detection register 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
000
Symbol
PRCR
Address
000A16
When reset
XXXXX0002
Bit symbol
Bit name
Function
RW
PRC0
Enables writing to system clock
0 : Write-inhibited
control registers 0 and 1 (addresses 1 : Write-enabled
000616 and 000716), oscillation stop
RW
detection register (address 000C16)
and CAN0 clock select register
(address 025F16)
PRC1
Enables writing to processor mode 0 : Write-inhibited
registers 0 and 1 (addresses 000416 1 : Write-enabled
RW
and 000516)
PRC2
Enables writing to port P0 direction 0 : Write-inhibited
register (address 00E216) and
1 : Write-enabled
CAN0 I/O port select register
RW
(address 00F816) (Note 1)
Reserved bit
Set to "0"
RW
Nothing is assigned.
In an attempt to write to these bits, write "0". The value, if read, turns out to be
indeterminate.
Note 1: 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 7.1 Protect register
Rev.1.00 Oct 20, 2004 page 40 of 222
REJ09B0007-0100Z