Teletype SA110 Description And Operation page 14

SECTION 578-200-100
TABLE B
ERROR INDICATION TIMING OPTIONS
STRAP STRAP
Tl T2
OUTPUT INH BETWEEN MIN ERROR
A B ADDED CAPACITOR* (Q2-Q3) (Q4-Q5)
PULSE ERROR IND IND INTERVAL
Closed Closed
None
500 MS 250 MS 250 MS 250 MS
500 MS
Closed Open
None 500 MS 3.5 MS 3.5 MS
496. 5 MS 500 MS
Open
Closed
None 1 MS 250 MS 250 MS 0
250 MS
Open
Open None
1 MS 3.5 MS 3.5 MS 0
3.5 MS
Open
Open 5 MFD Across 29-30
1 MS 65 MS 65 MS 0
65 MS
Open Open
2 MFD Across 29-30
1 MS
31 Ms
31 MS. 0
31 MS
*These values are shown for example only. Other durations for Tl and T2 are obtainable with other
capacitor values.
generating a line break or visually indicating the
error by actuating a low speed error counter and
lighting an indicator lamp, or lighting an indi-
cator lamp only.
3. 30 Because Q6 is normally off, the positive
potential at its collector holds output
amplifier Q7 off. The output of card MC405 at
terminal 11 thus is normally -14 volts. When
Q6 turns on, Q7 is turned on and its output rises
to +14 volts. Terminal 11 remains at this level
until Q6 turns off. This signal is used to advance
a high speed error counter!
3. 31
An
option is available to replace the coil
of relay Kl in the collector circuit of Q6
by a resistive load forcounter operationat 2400
baud. This is done by leaving strap C in and
removing strap D. It may not be desirable to
use this option in every case, however, because
it disables the indicator lamp. Refer to Fig-
ure 6 for the . timing for high speed operation.
(a) For 1050 baud operation (Part A), the
3. 5 ms output pulse is much shorter than
the 9. 52 ms character duration. (The ''blink"
option of the latching circuit inverts the out-
put pulse, but counter operation is not affected
except for the short delay before the counter
actuating pulse is generated.) Consequently,
the delay of roughly one millisecond at the
collector of Q6 due to the coil of relay Kl
(operate time 1 ms, release time 1 ms) has
no effect on the output at the collector of Q7
other than to delay each transition slightly.
This output is connected to a counter driver
which generates a negative-going pulse of 5
to 6 ms duration for every output pulse at Q7
to actuate the high speed counter.
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(b) For 2400 baud operation with the relay
coil in the circuit and the latching circuit
strapped for the blink option (Part B), the
duration of each character is only 0. 67 nis
more than the 3. 5 ms output pulse.
If
errors
are received consecutively, the 1 ms delay
cau·sed by the inductance of the relay coil pre-
vents the collector of Q6 from dropping to
0 volt onanyoutput pulse before the last. As
a result, only one pulse will be generated by
the counter driver - regardless of how many
consecutive errors are in the burst.
(c) If the latching circuit is bypassed and the
relay coil is strapped out of the circuit
(Part C), the output at Q7 is the same as the
3. 5 nis output pulse at Q5 (except for squarer
transitions), so an output to the counter driver
is produced for every error. The counter
driver cannot operate this fast, but produces
5 to 6 ·ms pulses at half the character rate.
However, there is an interval of only 3. 34
ms at most between consecutive pulses; the
high speed counter nominally requires a mini-
mum of 5 ms betweenactuatingpulses, though
most counters will operate correctly with a
somewhat shorter interval. Nevertheless,
this interval between pulses is probably too
short to allow most counters to reset fully
before being actuated again. Consequently
erratic operation can be expected when this
option is used, depending on the character-
istics of the particular high speed counter
furnished. The choice of option for 2400 baud
operation, therefore, depends on whether the
improvement in consecutive error counting
obtained is worth disabling the indicator lamp
to get.