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45
1.4.5.
Control
section
1.
4.5.1.
In terrup
t
con
trailer
Mode
switch
interrupts
The
four
mode
switches
SKI, SK2, SK3, SK4,
when
selected,
each
give
a
logic
0
pulse
via
Cl 91 9
to input
1
1
of the
3-in
put
NAN
D-gate
D
1
9
1
8.
Input
12
is
held
at logic
1
by
the pull-up
resistor
from
input
6 (INT)
of the
;UP.
When
there
is
no
input
from
the
trigger
level circuit,
input
1
3
is
also at logic
1
.
Consequently,
a
logic
0
pulse
from one
of
the
mode
switches
results
in
a
0
pulse
on
the interrupt input
INT.
During
a
timing
measurement,
the S'contact
when
switched
gives a logic
1
to the
pin
1
of
Schmitt
trigger
D1917,
which
gives a logic
0
pulse
via
Cl
91
2
to
reset
the
time measurements.
Trigger
level
interrupts
Interrupts are
also
generated
by
the
trigger
level circuit in
the timer
mode,
for starting
and stopping
the
pP
internal
counter during measuring.
The
functional
circuit
is
shown
in
Fig.
33.
Fig.
33. Interrupt controller
mitao
Permanent
non-interrupt condition;
Without
the timer
selected there
is
no output from
the
comparator
even
if
Hz
is
selected
because PI 6
inhibits
the
flip-flop
and
gives
a
'0'
on
NAND
input
2.
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