Teletype SA110 Description And Operation page 12

SECTION 578-200-100
indication triggers the one-shot multivibrators,
causing a positive-going pulse (-14 volts to +14
volts) to appear at the output and energize the
relay for the duration of the multivibrator time-
out period. This is accomplished as follows.
3. 24 Input amplifier Ql is normally on (col-
lector at 0 volt). When an error is de-
tected, the negative-going pulse ( +6 volts to 0
volt) at the output of the PE gate causes Ql to
become nonconductive.
3.25 Stages Q2 and Q3 formaone-shot multi-
vibrator whose timeout period is con-
trolled by R8, Cl, and C2. Transistor Q2 is
normally held off and Q3 is normally on. When
Ql is cutoff by the PE gate output, Q2 is brought
into conduction and a negative-going transition
is produced at the collector. This transition is
capacitively coupled to the base of Q3 by C 1 and
C2 or C2 alone. Stage Q3 is turned off and the
multivibrator begins its timeout.. The capacitors
or capacitor charge until the base of Q3 becomes
positive enough to allow it to conduct again. With
both capacitors in the circuit (factory wiring),
the timeout period of one-shot Q2-Q3 is approxi-
mately 500 milliseconds. Removing strap A so
that only C2 is in the circuit reduces the timeout
period to approximately 1 ms. An intermediate
timeout period can be obtained by removing strap
A and connecting a capacitor with a value between
those of Cl and C2 across terminals 27 and 28.
3. 26 Stages Q4 and Q5 also form a one-shot
multivibrator. Controlled by R14, C3,
and C4, its operation is the same as for one-
shot Q2-Q3. Stage Q4 reacts the same as Q2,
and Q5 the same as Q3; all four stages switch at
the same time initially. With both capacitors in
the circuit (factory wiring), the timeout period
ofone-shot Q4-Q5 is approximately 250 ms. Re-
moving strap B so that only C4 is in the circuit
reduces the timeout period to approximately 3. 5
ms. An intermediate timeout period can be ob-
tained by removing strap B and connecting a
capacitor with a value between those of C3 and
C4 across terminals 29 and 30. For example,
with a 5 microfarad (MFD) capacitor the time-
out will be approximately 65 ms, and with the 2
MFD capacitor {furnished with versions of the
SAll0 having an indicator assembly) the timeout
will be approximately 31 ms.
3. 27 The timeout period of one-shot Q4-Q5,
T2, controls the duration of the output
pulse and the time that the relay is energized.
If the timeout period of one-shot Q2-Q3, Tl, is
longer than T2, further triggering of one-shot
Page 12
Q4-Q5 will be inhibited· for a time equal to the
difference of the two periods. This timing is
shown in Figure 5, Case A. Since Tl is longer
than T2, the minimum interval in which repetitive
errors will be indicated is Tl and errors will not
be indicated during the inhibit period of Tl minus
T2.
If Tl is shorter
than T2, as shown in Fig-
ure 5, Case B, there is no inhibit period and the
minimum interval in which repetitive errors will
be indicated is T2. These relationships, and the
strapping required to obtain them, are summa-
rized in Table B.
3. 28 Despite the wide variety of timing options
available for special applications, most
SAl 10 installations use either the factory wiring
or have straps A and B removed, with or without
an added capacitor. The factory wiring provides
a 250 ms output pulse for generating a line break
(110 or 150 baud) or pulse on reverse channel
(1050 baud and higher speeds) wit;1 a 250 ms
inhibit before another error indication is made
to accommodate the response of the reverse
channel. (Normally the sender alarms on de-
tecting the line break or reverse channel pulse,
so additional error indications are not required.)
This wiring is also used when a lamp is to be
lighted on the first error which remains on until
reset. Removing straps A and B to eliminate
the error indication inhibit and reduce the output
pulse to 3. 5 ms allows a high speed counter to
record errors at the character rate at 1050 baud.
Adding a capacitor between terminals 29 and 30
with straps A and B removed allows a low speed
counter to record errors at the character rate
at 110 or 150 baud and error bursts at 1050 baud.
Note: The low speed counter supplied with the
SAll0 BB, SAll0 CB, and SAll0 EB re-
quires a minimum make duration (output
pulse) of 30 ms and a minimum break dura-
tion (delay between output pulses) of 30 ms.
With a 2 microfarad capacitor added between
terminals 29 and 30, the 31 ms output pulse
leaves a remainder of the character duration
at 150 baud of about 36 ms, permitting con-
secutive errors to. be registered at both 110
and 150 baud.
3. 29 Whatever its duration, the output pulse
from the collector of Q5 is passed to
relay driver Q6, either directly or through a
latching circuit. This relay driver is normally
held off (collector at +14 volts) by a low signal
from Q5 or the latching circuit. When the output
pulse is developed, Q6 turns on (collector at
0 volt) for the duration of the output pulse.
Normally relay Kl is energized while Q6 is on,