M16C Datasheet, PDF (32/262 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Preliminary Specifications REV.B
Mitsubishi microcomputers
Specifications in this manual are tentative and subject to change.
M16C / 6N Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
PBruosteCcotinotnrol
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 3-9 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), peripheral function clock select register
(address 025E16), CAN0/1 clock select register (address 025F16), serial I/O 3 control register (01E216), port
P7 direction register (address 03EF16) and port P9 direction register (address 03F316) can only be changed
when the respective bit in the protect register is set to “1”. Therefore, important outputs can be allocated to
port P7 or port P9.
If, after “1” (write-enabled) has been written to the port P7 or port P9 direction registers 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 When reset
000A16 XXXXX0002
Bit symbol
Bit name
PRC0
Enables writing to the system clock
control registers 0 and 1 (addresses
000616 and 000716), oscillation stop
detection register (address 000C16),
peripheral function clock select regis-
ter (address 025E16), and CAN0/1
clock select register (address 025F16)
PRC1
Enables writing to processor mode
registers 0 and 1 (addresses 000416
and 000516)
PRC2
Enables writing to port P7/9 direction
register (address 03F316 and 03EF16)
and SI/O3 control register (address
01E216) (Note)
Function
0 : Write-inhibited
1 : Write-enabled
0 : Write-inhibited
1 : Write-enabled
0 : Write-inhibited
1 : Write-enabled
RW
Nothing is assigned.
These bits can neither be set nor reset. When read, their contents are
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 3-9. Protect register
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