Teletype SA110 Description And Operation

BELL SYSTEM PRACTICES SECTJON 578-200-100
Plant Series Issue 1, September 1970
AT&TCo Standard
l
PARITY FAILURE DETECTOR (SAll0)
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DESCRIPTION AND PRINCIPLES OF OPERATION
CONTENTS PAGE
1. GENERAL .•.............
1
PHYSICAL CHARACTERISTICS . ; .. 5
ELECTRICAL CHARACTERISTICS .. 5
A. Input ................... 5
B. Output ................... 5
2.
GENERAL DESCRIPTION ..•..... 6
3.
PRINCIPLES OF OPERATION ..... 6
4.
VARIABLE FEATURES .......... 17
BYPASS SWITCH AND INDICATOR
ASSEMBLIES FOR 33 TYPE SETS ... 17
BYPASS SWITCH AND INDICATOR
ASSEMBLIES FOR 35 TYPE SETS ... 18
BYPASS SWITCH AND INDICATOR
ASSEMBLIES FOR "DATASPEED®"
RECEIVERS .................. 18
1.
GENERAL
1. 01 This section provides the description and
principles ofoperation for the SAll0 par-
ity failure detector ( Figure 1) and the bypass
switch and indicator assemblies available for use
with it (Figure 2). The variable features present
for the coded versions of the SAll0 are shown
on Table A. Refer to Section 578-200-200 for
installation information, Section 578-200-300
for checkout and troubleshooting procedures,·
and Section 578-200-800 for parts.
1. 02 The parity detector (SAll0) is an acces-
sory to a receiving data terminal. It
regenerates an incoming signal bit by bit and
monitors it for transmission errors. Upon de-
tecting an error, the parity detector supplies
either (a) an output to stop the sending terminal
or notify its operator or (b) an output
to
notify
the operator of the receiving terminal.
1. 03 The parity detector can be used with any
eight-level, serial-by-bit signal that
providesapa·ritybit, atany speed upto 2400baud
(2400 words per minute). It may be used with
either even or odd parity systems and with sig-
nals employing either 10-unit or 11-unit charac-
ter structure. The SAll0 can be applied to 33
and 35 type automatic send-receive or receive-
only terminals and Type 2 DATASPEED termi-
nals. No prearrangement with a sender is
necessary other than assurance of parity
transmission.
1. 04 Error detection is accomplished ahead of
the receiving terminal by checking each
incoming character for parity. Eight-level codes
provide a parity bit in addition to the seven in-
formation bits so that the total number of marking
bits in each character is always even, for even
parity, or odd, for odd parity. Characters re-
ceived with incorrect parity are detected as
errors.
1. 05 A supplemental error check based on
detection of displaced signal transitions
( significant distortion) is available as a strap op-
tion. The combination of this check and the parity
check increases the error detection capability of
the SAll0 but also increases the number of false
error indications received.
(a) The SAl 10 cannot detect every trans-
mission error when strapped for parity
checking alone because all characters with
two, four, six, or eight bits in error will have
correct parity; these characters will not be
recognized as errors. The SAllO will detect
approximately 75
to
80 percent of all trans-
mission errors when strapped for parity
checkingalone. Because all characters with
incorrect parity are detected as errors, a
false error indication will occur whenever the
Prepared for American Telephone and Telegraph Company by Teletype Corporation
©
1970 by Teletype Corporation
All rights reserved. ·
Printed in U. S. A. Page 1