# Bus Communication Troubleshooting

Most Voldeno Bus faults come from four causes: termination, voltage drop, topology violations, and a conductor in the wrong terminal. Work through the checks in order; each one is quick and rules out a whole class of problem.

# Match the symptom

Symptom	Check first
One module never appears in Studio	Supply voltage at that module, then its bus conductors
Modules drop out intermittently	Termination, then voltage drop under load
The whole bus is silent	Termination and topology
Errors appear only when relays switch	Voltage drop under load, supply sizing
Faults started after adding modules	Module count, bus length, supply headroom

# 1. Check termination

A bus needs exactly two terminations, on the first and the last module in the physical chain. Every module in between must have its switch OFF.

The switch is on the bottom of the enclosure on 4-DIN modules and on the right side on 2-DIN modules. Left is ON, right is OFF.

With the supply switched off, measure resistance across BUS+ and BUS−:

Reading	Meaning
~60 Ω	Correct: two 120 Ω terminations in parallel
~120 Ω	Only one end is terminated
~40 Ω	Three terminations; an intermediate module is switched on
Open circuit	No termination at all

Both under-termination and over-termination produce the same headline symptom, intermittent dropout, so measure rather than assume.

# 2. Check the supply at the module, not at the supply

A module that browns out under load looks exactly like a module with a bus fault. Read the terminal voltage in Voldeno Studio, or measure at the connector, at the module that is misbehaving and with every relay in that row energized.

If the reading sags only under load, the problem is distribution, not communication. Power supply sizing and distribution covers per-row feeds and conductor sizing.

# 3. Check the topology

The Voldeno Bus is a linear daisy chain. Three rules are absolute:

• No loops. The first and last modules must never be connected back to each other.
• No branches. Every module sits in one linear sequence; spurs off the main line are not allowed.
• No stubs longer than 1 m. A stub is any branch that does not lead directly to a module: test points, bypassed modules, intermediate resistor leads, power branches that are not part of the chain.

Violations cause signal reflections and corrupted CAN messages. The symptom is usually errors that get worse as traffic increases, which makes them look like a load problem.

# 4. Check the limits

Limit	Value
Modules per bus	40
Total bus length	300 m, first module to last
Stub length	1 m

If the fault appeared right after an extension, compare the installation against these numbers before looking anywhere else.

# 5. Check conductor placement

Each terminal pair has an Input (left) and an Output (right) position, and the pairs are easy to mix up when the connector orientation is inconsistent along a row.

Confirm that 24 V and GND are not landed on BUS+ or BUS−, and that the CAN pair is not reversed between two modules. Confirm each conductor is stripped to 9 … 10 mm and fully seated: a partially inserted push-in terminal reads as continuity but fails under vibration or thermal cycling.

# 6. Bisect the chain

If the checks above find nothing, split the problem in half. Disconnect the bus at roughly the midpoint, terminate the module that is now the last one in the remaining half, and power up.

• The half still on the bus works: the fault is in the disconnected half. Split that half again.
• It still fails: the fault is in this half. Split here instead.

Two or three iterations narrow a 40-module bus down to a single connection. Remember to restore the original termination switches once the faulty section is found.

# After the fix

Power on, wait 2-5 seconds for the modules to boot, and confirm in Voldeno Studio that every module appears in the connected devices list. Toggle one output to confirm communication works in both directions, then run a full system diagnostic from Studio.