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Page Title: Figure 6-38.--Rotary stepping switch selector.
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busy mark and send a busy signal to the calling party
function of the allotter (fig. 6-37) is to assign
(station 78).
linefinders to any of the line circuits as required. When
any line requests service, the allotter assigns a
SELECTOR.-- The selector in the MDM
linefinder to the call, then preselects the next idle
200/700 system is connected back to back with a
linefinder to be assigned to the next call. As busy
finder (linefinder); that is, each finder has its own
linefinders become idle, they are made available for
associated selectors witch. The selector locates an idle
allotment to any subsequent calls. When one XY
connector in the group of lines (switchboard) to which
switch is connected to a given position in the wire
a call is being made.
bank, no other XY switch in the system may connect
The MDM 200/700 system uses a 20-point,
to that position. The S lead of the XY universal switch
8-level, rotary switch as a selector (fig. 6-38). This
and the S wire bank are used to indicate the busy
switch may be stepped by pulses from the dial or be
condition. For example, if station 55 calls station 21,
operated in an automatic hunt sequence by using
a busy indicator, called a mark, is immediately
interrupter spring contacts. The rotary switch wiper
extended to position 55 of the S wire bank from the
moves after it has been released electronically; that is,
station 55 line circuit. After the associated connector
when the step magnet is operated, the wipers do not
XY switch has been stepped to position 21 of the wire
go into the next position until the step magnet is
bank (under the control of dial pulses from station 55),
released. In a typical commercial XY installation, the
a busy mark is applied to that position in the S wire
rotary switch is used with the allotter circuits.
bank from the connector. If any other station, say
However, in the MDM system, the rotary switch is
station 78, now tries to call station 55 or 21, the
used in the selector circuits.
associated connector XY switch will encounter the
Figure 6-38.--Rotary stepping switch selector.

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