M306V2EEFS datasheet(46/271 Pages) RENESAS

46 / 271 page

Rev.1.40

Oct 06, 2004 page 46 of 269

M306V2ME-XXXFP, M306V2EEFP

2.6 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 2.6.1 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 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

Symbol

Address

When reset

PRCR

000A16

XXXXX0002

Bit name

Bit symbol

0 : Write-inhibited

1 : Write-enabled

PRC1

PRC0

PRC2

Enables writing to processor mode

registers 0 and 1 (addresses 0004 16

and 000516)

Function

0 : Write-inhibited

1 : Write-enabled

Enables writing to system clock

control registers 0 and 1 (addresses

000616 and 000716

)

Enables writing to port P9 direction

(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 2.6.1 Protect register

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