
178
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2.1.2 Protect Operation
The following explains the protect operation. Figure 2.1.2 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 and system clock control register 1 to be in write-enabled state.
(2) The contents of system clock control register 0 and that of system clock control register 1 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) 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.
Operation
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:
(a) System clock control registers 0, 1 (addresses 0006
16
and 0007
16
)
(b) Processor mode registers 0, 1 (addresses 0004
16
and 0005
16
)
The values in registers (1) through (2) cannot be changed in write-protect state. To change values in
the registers, put the individual registers in write-enabled state.
(2) Protect register
Figure 2.1.1 shows protect register.
2.1 Protect
Figure 2.1.1. Protect register
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