AT&T Bell System 1A Manual page 8

$1CTION
252~
129-100
The status of the address bit designating the A
or B memory allows the on-line memory to be.
addressed. Two complete digit cycles (a print cycle
and a scan cycle) are completed in 512 microseconds.
Since input characters received from the data set
have a duration of 30 milliseconds and since 4.55
milliseconds are available for transferring data from
the memory to the output register, the interleaving
of print mode and scan mode digit cycles causes
no delay in data reception or printing functions.
2.26
Time-of-day, day-of-month, and month-of-year
data are required as header information for
each data-interval printout. The month-of-year
data is manually supplied to the equipment by the
operation of the CCU thumbwheel switches. The
remaining time data is provided by a digital clock
which is initially set to real time by the use of
switches and is clocked by the 60-Hz line. Scanner
number data is obtained from a print digit scan
counter in the printout control logic.
End-of-scans-completed data is accumulated for
each scanner in an associated locatio;n in memory
and is read out at the appropriate time in the print
cycle. The CCU number is read from a group of
gates which have handwired data inputs representing
the required number.
2.27
In normal operation, data accumulation and
printing are performed under the control of
the program timer which is used to establish the
required schedule. At the start of each printout
time, a scan/print enable signal is required from
the program timer to allow the continuation of
scanning and the initiation of another printout.
When scanning is permitted by the program timer,
a scan cycle is initiated every 100 seconds by
generation of the start-scan term supplied to .the
scan control from the printout . controL Each of
the 16 scanners is addressed for 6 seconds. Thus,
an entire scan cycle requires 96 seconds plus a
rest period of 4 seconds between successive scans.
During this rest period, the scanner number 1
input lines are connected to the data set. However,
an interrogate signal is not applied until the start
of the next scan cycle. ·
CONTROL PANEL LAMPS AND SWITCHES
A. Outside Cabinet Controls and Lamps
2.28
The CCU control panel (Fig. 6) is located
at the front of the CCU. The lamps, switches,
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controls, and pushbuttons for the CCU control panel
and their meaning and use follow.
RSU CHANNEL SELECT 1 Through 16 Lamps
2.29
Lighting of any·one of these 16lamps indicate
which of the 16 RSEU scan channels is being
selected for interrogation. If RSU CHANNEL
SELECT 1 lamp is continuously lighted, the CCU
is in an idle condition.
RSU CHANNEL ACTIVE/ ALARM 1 Through 16 Lamps
2.30
When an RSEU is selected for scanning (by
activation of its associated LOAD/IDLE/NO
LOAD switches), the associated ACTIVE/ ALARM
lamp lights dimly. If a selected RSEU fails
to
send an EOS code within an allowable time (5 1/3
seconds) after it receives an interrogate command,
the associated ACTIVE/ ALARM lamp lights brightly
indicating an RSEU failure. This condition will
continue until the ALARM RESET or MASTER
RESET pushbutton is operated.
LOAD/IDLE/NO LOAD 1 Through 16 Switches
2.31
When any LOAD/IDLE/NO LOAD switch is
set to LOAD, the associated RSEU input
pair is terminated in a 200-ohm load through
normally closed contacts of the associated scan
relay. When the associated relay is de-energized,
this completes the telephone circuit, thus maintaining
a dialed-up connection during periods when the
scanner input pair is not connected to the data
set. The switch set to LOAD also enables the
alarm logic associated with the channel. An alarm
indication is activated if the RSEU does not provide
an EOS signal within a 5-1/3 second period after
the removal of the start-scan command.
2.32
When any LOAD/IDLE/NO LOAD switch is
set to NO LOAD, no termination is provided
in the associated scanner input pair. The alarm
logic associated with the channel is enabled. In
addition, setting tlie switch to NO LOAD causes
the nearest lower-numbered scan relay (whose
LOAD/IDLE/NO LOAD switch set to LOAD) to be
activated in lieu of the scan relay normally associated
with the switch. Thus, if the RSEUs are connected
in tandem to one telephone pair, the CCU handles
the data as if each RSEU were independently
connected.
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