Teletype SA110 Description And Operation page 16

SECTION 578-200-100
3. 32 Bypassing the latching circuit is accom-
plished by leaving strap E closed and
opening straps F and G. This causes the output
pulse at the collector of Q5 to pass unchanged
to the base of Q6, energizing the relay or pro-
ducing an output to a counter driver as described
in 3.31 (c).
3. 33 The permanent latch option is obtained
by
leaving strap G closed and opening
straps E and F. This energizes relay Kl on the
fir st error detected and latches it in this state
until manually reset. This option is used for
the SAll 0 EC, which has an indicator lamp only,
to notify the operator that the received message
contains one or more errors.
(a) In the quiescent state, Q5 is normally
conducting and its collector is at approxi-
mately 0 volt. This signal is inverted
by
MLA-11 and connected to pin 10 of NANO
gate MLA-8 as
+6
volts. Pin 9 of MLA-8 is
also connected to +6 volts through resistor
R21, so the output of MLA- 8 is 0 volt, holding
Q8 off. The output of MLA- 8 is also connected
to pin 1 of NANO gate MLA-3, holding its
output high and the output of MLA- 6 low. This
low potential is applied to the base of relay
ddver
Q6
to hold it off.
(b)
When an error is detected, one- shot Q4-
'Q5 is triggered and its output, at the
collector of Q5, rises to
+6
volts. The output
of
MLA-11
then drops to 0 volt, which pro-
duces a high output at
MLA-8.
This positive
potential turns
Q8
on. Its collector potential
goes to approximately 0 volt (since 0 volt is
connected to the emitter from the indicator
~ssembly, via the manual reset switch and
terminal 9), supplying a low input to MLA-8
to maintain its output high after the collector
of Q5 returns to 0 volt. The high output from
MLA-8 causes the output of MLA-3 to be low
and theoutputof MLA-6high, turningonrelay
driver
Q6
and energizing the relay.
(c) Relay Kl remains energized - and the
indicator lamp remains on - until the
manual switch (in the lamp housing) is de-
pressed. This action opens a normally-
closed contact between the emitter of Q8 and
ground, raising the collector potential of Q8
to +6 volts. The output of MLA- 8 then drops
to 0volt, turning Q8 offandrestoring MLA-3
and MLA-6 to their quiescent states. This
turns off
Q6
and releases the relay.
Page 16
3. 34 The permanent latch with "blink" option
is programmed
by
opening strap E but
leaving straps F and G closed. Relay Kl is
energized for the first error detected and re-
mains energized until manually reset as for the
permanent latch option described above. Suc-
ceeding errors, however, cause the relay to
de- energize at the beginning of the output pulse
from Q5 and energize again at the end. The
indicator lamp is powered through the relay con-
tacts, so it turns on with the first error and
blinks off and on with each following er.ror. At
110, 150, or 1050 baud using the low speed
counter the blink is clearly visible, but at 1050
baud and higher speeds using the high speed
counter it usually is not. The low speed counter
is also driven
by
the relay contacts and advances
its count for each blink. The high speed counter
(not driven
by
the relay contacts) can record
consecutive errors at 1050 baud with this option,
even though the indicator lamp appears to be on
all the time.
(a)
In
the quiescent state, relay driver
Q6
is
held off as described in 3. 33 (a). When
an error is detected, one- shot Q4-Q5 is trig-
gered, the potential at the collector of Q5 goes
positive, and theoutputof MLA-11 drops to 0
volt. This low signal produces a high output
at MLA-8, which turns on Q8. Up to this
point operation is the same as for the perma-
nent latch option. With the blink option, how-
ever, the low output of MLA-11 is connected
to the other input of MLA-3, holding its output
high. The resulting low output at MLA-6 holds
relay driver
Q6
off, keeping the relay de-
energized.
(b)
At the end of the Q4-Q5 timeout period,
the collector of Q5 returns to 0 volt and
the output of MLA-11 becomes high again.
This signal causes the outputs of MLA-3 to
go lowand of MLA-6 toga high, turningrelay
driver
Q6
on and energizing the relay. The
relay is latched on by the output of Q8, via
MLA-8, MLA..:3, and MLA-6. Whenone-shot
Q4-Q5 times out on succeeding errors, the
output of MLA-11
will
drop from high to low
for the duration of the timeout period. This
change is applied to an input of
MLA-3,
pro-
ducing a corresponding change at
MLA-6
and
Q6.
As a result, the relay is de-energized
at the beginning of the timeout period and re-
energized at the end.
3 .. 3 5 The SAll 0 has a built- in lamp test feature
for applications in which a lamp is driven
by the relay contacts. By connecting a normally-