Introduction - Fermax MDS-2H Manual De Instrucciones

Decoder MDS-2H
Decoder MDS-2H

INTRODUCTION

This device is an interface between the MDS bus (+, -, D1, D2, 2, 6) and the new 2-wire telephones or other 2-wire
devices that may appear in the future. It is a floor distribution device and from the point of view of an MDS minicentral it
behaves the same as the other Fermax decoders.
In particular, utilised jointly with said telephones (monitors), the system integrates the functions of telephony and alarm
management, as the 2-wire phone can handle up to 4 sensor inputs.
Its main function is to adapt a 6-wire technology (two for supply, two for data and another two for audio) to a 2-wire
technology (Sx terminals,-), where audio, data and supply are transmitted by the same 2 wires without polarity. Basically,
it carries out an adaptation both of the protocols that intervene in each segment and of the audio signals. The main
advantage provided is simpler installation of the device in buildings.
This decoder is prepared to link up 4 or 8 2-wire user devices (4 and 8 line models, respectively). The 2-wire section,
from a logical point of view, is a bus and from the physical angle has a star topology.
This enables the decoder to isolate each of the 2-wire devices connected, so that a fault in one of them will not
interfere with the smooth running of the rest of the installation. When the decoder detects a line fault (for example a short
circuit, anomalous function of a telephone, attempted sabotage, etc.), it disconnects it from the installation and sends the
relevant warning to the central unit.
The 8-line decoder comes with 8 cards (4 for the 4-output version), vertically mounted (one for each output), whose
function is that of isolating the device linked to that output from the rest of the equipment connected to the decoder. In
addition, next to each terminal is an LED (DL5..DL12) that signals line disconnected (when lit).
In normal operation (when there is no audio), the decoder does a polling (survey) of the devices connected to it. If a
device does not respond, a short circuit is forced in the line, causing the device to reset. If it still does not respond, we
deduce that there is a serious problem (fault, sabotage ...), isolating said output and notifying central of this event.
(These warnings can be viewed if there is a panic guard unit). Periodically, it will attempt to connect with the isolated
devices, in case the problem has been resolved. In this way, the decoder-telephone section is protected against short
circuits and wire cuts.
To protect the MDS bus against possible sabotage attempts, the minicentral (version 5.0) periodically checks the
state of an installation decoder, which, to afford greater protection, will be further away (to reach it you have to go through
the whole MDS bus). The decoder to be tested can be selected from the outdoor panel.
It also has an additional relay, general purpose terminals C (common), R (active output), with switch configurable
NA/NC output. This relay may be activated from the telephones connected to the decoder. The relay may also be used
to connect a siren, for example. Working this way, the relay would be activated for the set time when the decoder
intercepts an alarm message coming from one of the telephones linked to it or when it detects a line fault. Relay
functionality selection is configurable (activation of this relay may be programmed from any telephone linked to the
decoder. Relay functionality selection (activation by means of a telephone push button or by detection of an alarm
message) is configurable. Timing of this relay can be programmed from any telephone connected to the decoder.
This decoder, utilised jointly with video distributors (Ref. 2418, 2419), permits video door entry installations with 2-wire
telephone features. In this type of installations, each decoder installed will have an associated video distributor, both
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