Timer Feature Operational Characteristics; Interrupts; Interrupt Presentation - IBM Series 1 User Manual

TIMER FEATURE OPERATIONAL CHARACTERISTICS
Condition Codes Reported at Interrupt Time
The interrupt condition codes (ee) are listed and described
in this section to aid in the understanding of interrupt
presen·ta tio n.
ee2
CC3
CC4
CC6
CC7
2
3
4
6
7
Meaning
Exception
Device end
Attention
Attention and exception
Attention and device end
~.!.£g£1iQ!l - An overrun condition has occurred in
the timer. Overrun means that a device end
interrupt condition occurs while a previous device
end interrupt is still pending in the timer.
Qev.!£g
Eng
Reported when the timer has
decremented one more than the specified number of
time intervals (underflow). Also reported when
the external gate has been enabled and the timer
detects an underflow prior to the end of one
complete external gate cycle.
Attention - Reported only when an
cycle has been completed prior
underflow. The run state is reset.
external
to a
gate
·timer
!
ttentiQ!! ~g
E.x£££.?ti.Q!! -
Reported if the external
gate cycle has been completed and an overrun
condition is present in the timer. The run state
is reset. (See CC2).
!.ttentiQ!!
~nd Q~i£~ ~.!!.g
-
Reported when a timer
has underflowed prior to, or at the same time as,
the completion of an external gate cycle. The run
sta te is reset.
Interrupt Presentation
The timers are prepared together and function as one
preparable source. Neither timer should be started unless
the I-bit is on.
After starting, the timers post the first device-end
interrupt in a time interval corresponding to the specified
count up to a maximum of one more count. For example,
if
a
count of hex 000] were loaded (3 counts), the actual time to
3-8 GA34-0033
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