IBM 2790, Manual

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2790 A D A P T E R
The 2790 adapter controls the high-speed (approximately
500,000 bits per second) transmission loop. The loop is
divided into four segments at the 2790 adapter; each seg­
ment has its own connections to the adapter. Data from
each segment is normally fed to the next segment in the
loop. However, any combination of segments may be by­
passed under user or diagnostic control.
Data-Handling Capacity
The 2790 adapter can concurrently receive input data from
eight different area stations, and send output data to five
different area stations.
The number of data entries per second that the 2790
system can handle depends on the type of data entry and if
the delete-blanks option is activated on the area station.
The following set of formulas provides a method of comput­
ing the peak use of the 2790 transmission line for a given
data traffic. Figure 23 shows some of the formulas in chart
form. The chart and formulas will aid the user in determin­
ing whether his peak traffic exceeds the transmission-line
capacity. If peak traffic exceeds the line capacity, the user
may want to place limitations on nonpreferred traffic during
periods of peak preferred traffic or he may locate preferred-
traffic terminals first on the transmission-line loop.
Note: Utilization of the 2790 transmission line loop
may be degraded if the 2715 to System/360 data link
is not adequate to service priority data. Deferred data
is automatically stored on 2715 disk and does not affect
utilization-degradation considerations. If the 2715 to
System/360 data link is permanently down, all priority
data is stored on the 2715 disk without degrading the
loop utilization. When the 2715 disk is filled, the 2790
system is brought to a soft stop, the alarm sounds, and
catalog number X‘9C’ is displayed.
The user can bypass and restore segments of the 2790
adapter loop or individual area stations under control of
messages received at the 2715. These messages can be sent
from System/360 or from the 2715 CE/operator panel. Thus
the System/360 can dynamically bypass and restore 2790
terminals to provide priority for preferred traffic.
For example, a user with a time-attendance application
may have a requirement that all employees clock out during
a specified time interval. Possibly other data traffic com­
bined with attendance-recording traffic may exceed full­
load traffic for a short period of time, thus increasing the
time required to clock out the employees. If the graph and
formulas show that this is likely, the user may request that
other employees not enter nonattendance data during the
attendance-recording period, or the System/360 can tem­
porarily bypass those area stations not used for attendance
and restore them after completion of the attendance period.
Badge Reading on 1035—Delete Blanks Activated on 2791
% Utilization (1035) = (N + 4) 0.128 x entries/second
where N=number of punched badge positions
Badge Reading on 1035—Delete Blanks Not Activated on
2791
% Utilization (1035) = 1.79 x entries/second
Badge Reading on 2791 Resident Badge Reader—
Delete Blanks Not Activated
% Utilization (2791 RB) = (N + 5) 0.128 x entries/second
where N=number of punched badge positions
Badge Reading on 2791 Resident Badge Reader-
Delete Blanks Activated
% Utilization (2791 RB) = 1.92 x entries/second
Keyboard Entries from 2791 Keyboard
% Utilization (2791 K) = 1.41 x entries/second
Card Entries from 2791 Card Reader
% Utilization (2791 CD) = (0.219N + 0.64) x entries/sec.
where N=number of columns scanned from card up to
and including EOC character. N=83 if EOC is not
present
Entries from Data Entry Units
% Utilization (2795/2796) = 7.27 x entries/second
Total Utilization
Total utilization equals the sum of the individual utilizations.
If total utilization reaches 100%, requests for data entries in
excess of
100
% will be serviced when prior read operations
are completed. When data entry requests exceed 100%
utilization, the area stations at the beginning of the
transmission-line loop will be serviced before stations at
the end of the loop.
Utilization Examples
Example 1. Assume the user wants to clock out 5400
employees in three minutes (30 employees per second) using
sixty 1035 Badge Readers (Delete Blanks off).
% Utilization = 1.79 x 30 = 53.7%
Thus, allowing two seconds per badge entry, the 30 clock-
outs per second can be obtained at a walk-by rate of 30 per
badge station per minute if other system requirements do
not exceed 46.3% of the system utilization. The 46.3%
would allow three 56-column cards and one 2796 data entry
to be read during the same second without affecting the
badge-reading rate. Should more than 46.3% of read time
occur, and depending on physical placement of the terminals
IBM 2715 Transmission Control Unit 39