PiXtend eIO Hardware Manual
If the modules are spatially separated in a network or it is necessary to use several power
supplies for the entirety of the bus participants for other reasons, the ground (GND) of all
power supplies must be connected to each other at a central ground point via a suitable
cable - equipotential bonding.
In the following figure 2 we show you typical wiring errors with regard to the power supply
of the modules.
At first glance, it may make sense to "bridge" / "looping" the supply voltage and GND from
one module to the next. However, this leads to voltage drops on the lines, especially when
using small conductor cross-sections and many devices. The result may be that the
required minimum voltage is no longer applied to a part of the modules and the devices do
not or no longer fully fulfill their function.
A particularly serious error occurs when the GND line is "saved" at the supply connection.
One could come up with this idea, since already at the RS485 connections a GND
connection is made. However, the supply current of the modules must under no
circumstances be routed via this connection.
Transmission errors, incomprehensible communication behavior and possibly overloading,
usually thin bus lines, can be caused by this.
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Figure 2: Topology of the power supply - typical errors
