User’s Manual
C166S V1 SubSystem
Central Processing Unit
User’s Manual
3-79
V 1.6, 2001-08
be reasonably used for table search operations. In all other cases, the E-flag value
depends on the value of the source operand to signify whether or not the end of a
search table is reached. If the value of the source operand of an instruction equals the
lowest negative number that depends on the data format of the corresponding
instruction (8000
H
for the word data type, or 80
H
for the byte data type), the E-flag is
set to 1; otherwise it is cleared.
• MULIP-Flag: The MULIP-flag will be set to 1 by hardware upon the entrance into an
ISR when a multiply or divide ALU operation was interrupted before completion.
Depending on the state of the MULIP bit, the hardware decides whether a multiplication
or division must be continued or not after the end of an interrupt service. The MULIP bit
is overwritten with the contents of the stacked MULIP-flag when RETurn-from-Interrupt-
instruction (RETI) is executed. This normally means that the MULIP-flag is cleared again
after that.
Note: The MULIP flag is a part of the task environment. When the ISR does not return
to the interrupted multiply/divide instruction (e.g. in case of a task scheduler that
switches between independent tasks), the MULIP flag must be saved as part of
the task environment and must be updated accordingly for the new task before this
task is entered.
CPU Interrupt Status (IEN, ILVL)
The Interrupt ENable (IEN) bit makes it possible to enable (IEN=1) or disable (IEN=0)
interrupts globally. The four-bit LeVeL field (ILVL) specifies the priority of the current
CPU activity. The priority level is updated by hardware upon entry into an ISR, but it can
also be modified via software to prevent other interrupts from being acknowledged. If an
priority level 15 has been assigned to the CPU, it has the highest possible priority, and
thus the current CPU operation cannot be interrupted except by hardware traps or
external non-maskable interrupts. For details, please refer to
Section 3.4
“Interrupt and
Trap Functions” .
After reset, all interrupts are disabled globally, and the lowest priority (ILVL=0) is
assigned to the initial CPU activity.
Содержание C166S V1 SubSystem
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Страница 16: ...User s Manual C166S V1 SubSystem Introduction User s Manual 1 6 V 1 6 2001 08...
Страница 126: ...User s Manual C166S V1 SubSystem Central Processing Unit User s Manual 3 96 V 1 6 2001 08...
Страница 178: ...User s Manual C166S V1 SubSystem Memory Organization User s Manual 4 52 V 1 6 2001 08...
Страница 206: ...User s Manual C166S V1 SubSystem Instruction Set User s Manual 5 28 V 1 6 2001 08...
Страница 306: ...User s Manual C166S V1 SubSystem Detailed Instruction Set User s Manual 6 100 V 1 6 2001 08...
Страница 362: ...User s Manual C166S V1 SubSystem The External Bus Interface User s Manual 8 40 V 1 6 2001 08...
Страница 452: ...User s Manual C166S V1 SubSystem General Purpose Timer Unit User s Manual 12 44 V 1 6 2001 08...
Страница 454: ...User s Manual C166S V1 SubSystem Instruction Index User s Manual 13 2 V 1 6 2001 08...
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