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22 FUJITSU MICROELECTRONICS LIMITED CM71-00105-1E
CHAPTER 3 PROGRAMMING MODEL
3.3
3.3.5 Interrupt Level Mask Register (ILM)
Interrupt level mask register (ILM) is a 5-bit register used to store the interrupt level mask value. It lies
between bit20 to bit16 of the program status (PS).
Figure 3.3-5 shows the bit configuration of interrupt level mask register (ILM).
Figure 3.3-5 Interrupt Level Mask Register (ILM) Bit Configuration
The value stored in interrupt level mask register (ILM), is used in the level mask of an interrupt. When the
interrupt enable flag (I) is "1", the value of interrupt level mask register (ILM) is compared to the level of
the currently requested interrupt. If the value of interrupt level mask register (ILM) is greater (interrupt
level is stronger), interrupt requested is accepted. Figure 3.3-6 shows the functions of interrupt level mask.
Figure 3.3-6 Functions of Interrupt Level Mask
The values of interrupt level range from 0(00000
B
) to 31(11111
B
). The smaller the value of interrupt level,
the stronger it is, and the larger the value, the weaker it is. 0(00000
B
) is the strongest interrupt level, while
31(11111
B
) is the weakest.
There are following restrictions on values of the interrupt level mask register (ILM) that can be set from a
program.
• When the value of interrupt level mask register (ILM) lies between 0(00000
B
) to 15(01111
B
), only values
from 0(00000
B
) to 31(11111
B
) can be set.
• When the value of interrupt level mask register (ILM) lies between 16(10000
B
) to 31(11111
B
), only
values between 16(10000
B
) to 31(11111
B
) can be set.
• When setting of values between 0(00000
B
) to 15(01111
B
) is attempted, 16 is added on automatically and
values between 16(10000
B
) to 31(11111
B
) are set.
The interrupt level mask register (ILM) is initialized to 15(01111
B
) following a reset. If an interrupt request
is accepted, the interrupt level corresponding to that interrupt is set in the interrupt level mask register
(ILM).
For setting a value in interrupt level mask register (ILM) from a program, the STILM instruction is used.
bit20 bit19 bit18 bit17 bit16
ILM4 ILM3 ILM2 ILM1 ILM0
Initial value
01111
B
Interrupt controller
Interrupt activated
Peripheral
Interrupt
request
Activation OK
ICR
25
ILM
29
Comp
29>25
1
FR81 family CPU
AND