SR05-D1A3-PV manual v1801 33/83
5.8 Using SR05-D1A3-PV’s digital output
SR05-D1A3-PV can be read out either via its digital output or via its analogue output.
When opting for the analogue output, please refer to the next section. This section
describes how to use the digital output. When using SR05’s digital output, SR05-D1A3-PV
can be connected to an RS-485 network. How to communicate with SR05, and the
Modbus protocol, is described in chapter 6.
5.8.1 Connecting SR05-D1A3-PV to an RS-485 network
SR05-D1A3-PV is suited for a two-wire (half-duplex) RS-485 network. In such a network
SR05-D1A3-PV acts as a slave, receiving data requests from the master. An example of
the topology of an RS-485 two-wire network is shown in the figure below. SR05-D1A3-PV
is powered from 5 to 30 VDC. The power supply is not shown in the figure. The VDC [-]
power supply ground must be connected to the common line of the network.
Figure 5.8.1.1 Typical topology of a two-wire RS-485 network, figure adapted from:
Modbus over serial line specification and implementation guide V1.02 (www.modbus.org).
The power supply is not shown in this figure.
After the last nodes in the network, on both sides, line termination resistors (LT) are
required to eliminate reflections in the network. According to the EIA/TIA-485 standard,
these LT have a typical value of 120 to 150 Ω. Never place more than two LT on the
network and never place the LT on a derivation cable. To keep the RS-485 bus in a well
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