Vers. No. 6.1
136 Released: 25/04/2017
6 Functional Procedures → Using serial interfaces
You can connect both converters to any “normal” RS-232 inter-
face, e.g. your PC, and then communicate with the Q.bloxx mod-
ules (UART connectors) via the RS-485 interface.
6.1.2 Bus termination on the Q.bloxx modules
To avoid signal reflections on the RS-485 interface lines each sec-
tion (bus segment) must be terminat
ed at its physical start and
end with a certain resistance. To achieve this, a terminating
resistance is connected between the bus lines A (UART A) and B
(UART B). The line A is then connected via a pull-up resistor to
the supply voltage potential (Supply +10 to 30 V
DC
) and line B is
connected to the Supply 0 V through a pull-down resistor. These
three
resistors ensure an interference-free data transmission and
provide defined potentials (voltage levels) when no data is being
transmitted over the bus (the interface).
The sockets on the Q.bloxx modules already have these resistor
s
built in. You activate the resistors via the DIP switches 9 and 10;
in this way both bus lines are connected to the resistance circuit.
➡ If the base is intended for accepting a Q.gate module, the termi-
nating resistances must not be activate
d, because this module
contains its own resistances.
The terminating resistances may only be activated at the end
points of the interface line (of the bus segment). If resistances are
also activated in between, the signal is weakened and interfer
-
ence or even interruption of the data transmission occurs for the
modules located after the additional resistances.
6.1.3 Connection technology
With strong ambient interference, as is often found in industrial
areas, we recommend screening the bus and signal lines. Gener-
ally, you should always wire the screen t
o the earth conductor/
housing and not to the circuit ground. If necessary, the screen
can also be connected to the protective earth several times along
the cable route for potential equalization. With short distances,
e.g. stub lines, better results are often achieved when the screen
is only connected to the end of the stub line.
With bus devices such as controllers (PLCs),
computers (PCs),
re
peaters, interface converters, etc. the screen is usually realized
by the protective conductor, in some cases using special chassis
ground buses. Due to the screen, interference signals are
diverted through the protective conductor before they can pene-
trate into the module. The screen on the bus cable is in this case
connect
ed via so-called screen terminals. Similarly, connect the
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