Network Controllers Manual
45
SO-20 Serial Option to 20mA Loop Module
Description
The SO-20 Serial Option to 20 mA loop interface module, when used in
conjunction with the COMM-3S serial communications card, is designed
to connect network components via a 20 mA communications loop. 20
mA communications loops are suitable for long distance use where 22 to
26 gauge telephone wiring is available. This supervised network
communications loop is configured as a Class B (Style 4) loop or Class A
(Style 7) (use an SO-20D or two SO-20's) and is capable of
communications rates up to 9600 Baud, depending on line length and
installation.
Two red LEDs verify communications on the data out (send) and data in
(receive) lines. Communications failure is annunciated via the network.
Bypass mode lets signals pass through the module in the event of power
loss. This insures network integrity in the event a field panel should
experience a power failure and lose battery backup.
The SO-20 circuitry is protected from line surges and voltage spikes by
integral on-board protection devices.
TB1
TB3
TB2
P3
J3
J4
P1
P2
J1
J2
24V COM EARTH
DATA
IN
DATA
OUT
+
+
+
-
-
[NWC-019.CDR]
SO-20 Module
Application
The SO-20 module connects to the CM1(N) w/SO Option, the RMDP-
1N w/SO Option, and the CM2(N) w/SO Option using a 10 conductor
ribbon cable (P/N 250099) which terminates on the COMM-3S Serial
Communications Card (P/N 130144). The COMM-3S card plugs into
control module mother board communications slot P3. When an
COMM-3S card is used, the RS-232C signal is available on control
module mother board terminals 1-4, TB-1.
Note:
Regenerative network capability is not compatible with COMM-
3S card communication (20mA Loop and Fiber Optic Link) protocol.
The ACP(6) audio control panel (via the ACP CPU Card), the SAN
and RASP annunciators (via the SAN CPU and REM cards
respectively); the IRC-1, and the MST may be connected to the IRC-3
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