Northern Telecom DMS-100 Series General Description, Installation And Maintenance page 29

PRACTICE 297-2011-200
Page 2-22
power (LP) or alternate power (AP) supply conditions, the other is used to
adjust the set to loop powering the set only (LO), or for loop powering one
set and one 20 button add-on unit (HI).
•
The S3 Switch is used to select the operating mode of the set. In the
MAIN set position, the set is a 900 Ohm ac impedance and draws loop
current. In the EXTension position, the set is a high impedance and does
not draw loop current.
2.18 Business sets with alphanumeric display have four option
switches: S1, S2, S3, and S4. These switches perform the following
functions:
• The S1 Switch is used to select the operating mode of the set. In the
MAIN position, the set is a 900 Ohm ac impedance and draws loop
current. In the EXTension position, the set is a high impedance and
does not draw loop current.
• The S2 Switch is used to change the loop current drawn by the set.
When set to SHORT (loop length less than or equal to 250 Ohm), both
the set and the display are loop powered; when set to LONG (loop
length greater than 250 Ohm), an alternate power supply is required to
operate the alphanumeric display.
• The S3 Switch is used to test the display screen. During normal
operations (i.e. when set is not in the display screen test mode), both
toggles must be in the OFF position.
concerning test routines, refer to Part 3 (Verification Procedures).
•
The S4 Switch is used to set the address of the set. Address 0 is
reserved for the main set, address 4 is reserved for possible extensions.
Presently, extension sets are not in use, and are not supported.
2.19 Option Switch Settings: For a listing of internal option switch
settings for business sets, refer to Table 2-C. Associated illustrations are given
in Fig. 2-13, and 2-15.
2.20 20-Key/16-LCD Indicator Add-on modules are equipped with
two option switches: S1 and S2. These switches perform the following
functions:
• The S1 Switch is used to set the address of the 20-button add-on unit.
Addresses 1, 2, and 3 are reserved for the respective add-on units to a
main set; addresses 5, 6, and 7 are reserved for add-on units 1, 2, and 3,
respectively, to an extension set. Presently, extension sets are not in
use, and are not supported.
• The S2 Switch is used to switch the power supply for the add-on unit
between loop power (LP) and alternate power (AP) from an external 24
Vdc supply.
For further information