M16CSLASH62 datasheet(65/621 Pages) RENESAS

65 / 621 page

Mitsubishi microcomputers

M16C / 62 Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

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 1.13.6 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), port P9 direction register (ad-

dress 03F316) , SI/O3 control register (address 036216) and SI/O4 control register (address 036616) can

only be changed when the respective bit in the protect register is set to “1”. Therefore, important outputs

can be allocated to port P9.

If, after “1” (write-enabled) has been written to the port P9 direction register and SI/Oi control register

(i=3,4) 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 000416

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

control register (i=3,4) (addresses

036216 and 036616) (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 1.13.6. Protect register

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