7700 MultiFrame Manual
7707DT RS-232/422/485 Fiber Data Transceiver
Page - 26
Revision
1.8
7.2. INTERFACE
METHODS
From the above overview, it is apparent that special considerations are required when connecting MPK
interface signals to the RS-422 or RS-485 interface of the 7707DT. The issue at hand is the high-
impedance state that each Control Panel assumes between data transmissions. If several control panel
outputs are to be connected together, then this high-impedance state is required to avoid contention of the
shared output connection. The RS-422 interface protocol does not accommodate a high-impedance output
state. The RS-485 interface protocol does support this high-impedance output state, but only
accommodates a single balanced connection per signal channel. The below two sections describe special
requirements for connecting the MPK interface to the RS-422 or RS-485 interfaces of the 7707DT.
7.2.1. MPK Interface to RS-422
The RS-422 interface format does not accommodate a high-impedance output state. The MPK interface
signal can, however, be connected to the RS-422 interface of the 7707DT. While the input to the 7707DT
is in a high-impedance state, the respective output of the companion 7707DT will assume a known logic
state. By this method the MPK signal will be converted to an RS-422 signal, and the high-impedance state
will be converted to a known logic state.
MPK data from one or more Control Panels can therefore be transported across the RS-422 interface of
the 7707DT. The System Controller must have an independent connection to the RS-422 interface of one
7707DT. All Control Panels sharing that System Controller port must reside on the respective RS-422
connection of the companion 7707DT. If any Control Panel is connected to the 7707DT interface that is
local to the System Controller, the output signals of the 7707DT and that Control Panel will conflict by
outputting data to the shared signal connections at the same time.
Serial data channels used for this interface method should be configured for RS-422 at both ends of the
7707DT fiber link. Figure 7-4 and Figure 7-5 describe correct and incorrect interface methods,
respectively. Figure 7-6 describes pin-for-pin connections for the correct method.
7707DT
Control Panel
Control Panel
Control Panel
Jupiter System Controller
7707DT
Set to
RS-422
Set to
RS-422
Figure 7-4: MPK Interface to RS-422 - Correct Method
