Renesas M16C Series User Manual

Protect
M30240 Group
Rev.1.00 Sep 24, 2003 Page 140 of 360
2.1 Protect
2.1.1 Overview
'Protect' is a function that causes a value held in a register to be unchanged even when a program runs
away. The following is an overview of the protect function:
(1) Registers affected by the protect function
The registers affected by the protect function are:
• System clock control registers 0, 1 (addresses 0006
16
and 0007
16
), Frequency synthesizer registers
(address 03DB
16
to 03DF
16
)
• Processor mode registers 0, 1 (addresses 0004
16
and 0005
16
)
The values in these registers cannot be changed in write-protect state. To change values in the reg-
isters, put the individual registers in write-enabled state.
(2) Protect register
Figure 2.1 shows protect register.
Figure 2.1: Protect register
2.1.2 Operation
The following explains the protect operation. Figure 2.2 shows the set-up procedure.
(1) Setting “1” in the write-enable bit of system clock control registers 0 and 1 causes system clock
control register 0, system clock control register 1, and the frequency synthesizer registers (FSCCR,
FSC, FSM, FSP, FSD) to be in write-enabled state.
(2) The contents of system clock control register 0, system clock control register 1, and the frequency
synthesizer registers are changed.
(3) Setting “0” in the write-enable bit of system control registers 0 and 1 causes system clock control
register 0 and system control register 1 to be in write-inhibited state.
(4, 5, 6) To change the contents of processor mode register 0 and that of processor mode register 1,
follow the same steps as in dealing with system clock control registers.
Protect register
Symbol Address When reset
PRCR 000A16 XXXXX0002
Bit name
Function
Bit symbol
b7 b6 b5 b4 b3 b2 b1 b0
PRC1
PRC0
Enables writing to system clock registers
0 and 1 (addresses 0006
16, 000716) and
frequency synthesizer registers
(addresses 03DB16 to 03DF16)
W
R
Reserved bit
Always set to "0"
Enables writing to processor mode
registers 0 and 1 (addresses 0004
16
and
0005
16
)
0 : Write-inhibited
1 : Write-enabled
0 : Write-inhibited
1 :
Write-enabled
Nothing is assigned. These bits cannot be set or reset.
The value is indeterminate when read.
0

Renesas M16C Series Specifications

General

Brand	Renesas
Model	M16C Series
Category	Computer Hardware
Language	English