M16CSLASH1N datasheet(52/238 Pages) RENESAS

52 / 238 page

Rev.1.00

Oct 20, 2004

page 40 of 222

M16C/1N Group

7. Protection

REJ09B0007-0100Z

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".

Enables writing to system clock

control registers 0 and 1 (addresses

000616 and 000716), oscillation stop

detection register (address 000C16)

and CAN0 clock select register

(address 025F16)

Enables writing to processor mode

registers 0 and 1 (addresses 000416

and 000516)

Enables writing to port P0 direction

CAN0 I/O port select register

(address 00F816) (Note 1

)

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.

Protect register

Symbol

PRCR

Address

000A16

When reset

XXXXX0002

Function

Bit name

Bit symbol

PRC0

0 : Write-inhibited

1 : Write-enabled

PRC1

0 : Write-inhibited

1 : Write-enabled

PRC2

0 : Write-inhibited

1 : Write-enabled

Reserved bit

Nothing is assigned.

In an attempt to write to these bits, write "0". The value, if read, turns out to be

indeterminate.

Set to

"0"

00 0

Figure 7.1 Protect register

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