20
Installation
DIP Switch
1
2
3
4
5
6
7
Up
(1) Value
1
2
4
8
16
32
64
Address
Examples
1
Up
Down Down Down Down Down Down
1+2+4 = 7
Up
Up
Up
Down Down Down Down
4+16 = 20
Down Down
Up
Down
Up
Down Down
1+2+16+32+64 = 115
Up
Up
Down Down
Up
Up
Up
Table 3: Modbus Address Selection
For example, if DIP switch positions 3 and 5 are in the 1 (up) position and the rest are 0 (down),
the resulting Modbus address is 4 + 16 = 20.
Once you are communicating with the meter, you can change the address using either the DIP
switches or the
register.
Setting all DIP switch positions to zero for ten seconds resets all communication settings to the
factory configuration. If you ordered communication options like
Option EP
, they will be applied.
This can be useful if you cannot communicate and need to return the meter to a known state.
Option AD
The WattNode Modbus meter can be ordered from the factory with the Modbus address pre-
programmed to any value from 1 to 247 using
Option AD=xxx
where
xxx
is the desired address.
If you want to change the address of a meter with Option AD, there are two options:
1)
Set the address with the DIP switch:
Set the DIP switches to the desired address, then
write 0 to the
register (to override the factory programmed address). Finally,
write 1234 to the
register to apply the new address.
2)
Set the address with the
Address
register:
Set the DIP switches to any non-zero address
so the meter won’t reset the address to the factory programmed value. Next write the new
address to the
register. Finally, write 1234 to the
register to apply the change.
Baud Rate
Select the baud rate by setting DIP switch position 8 as shown below. The change will take effect
immediately. The baud rate can be programmed by the factory with
Option 19K
(19,200 baud)
or
Option 38K
(38,400 baud), in which case, DIP switch 8 has no effect. You may also use the
register to reprogram the baud rate from 1,200 to 38,400 baud.
Baud Rate
DIP Switch Position 8
9,600 (default)
0 (down)
19,200
1 (up)
Table 4: Baud Rate Selection
Connecting Modbus Outputs
The Modbus WattNode meter communicates using a serial EIA RS-485 interface. The meter uses
half-duplex two-wire (plus common) communication, so the same pair of wires is used for send-
ing AND receiving. Up to 127 devices can be connected together on the same RS-485 bus (or up
to 247 devices if you assign Modbus addresses using the
Address
register).
Planning the Modbus Network
EIA RS-485 networks should always be wired in a bus (or daisy-chain) configuration. In other
words, the bus should start at the PC, Modbus master, or monitoring device and then run to each
meter in turn. Try to avoid branches, and avoid home-run wiring (where each meter has its own
