A-46
MODEL 2700 APPENDIX A
MODBUS PROTOCOL
2.4 MODBUS TROUBLESHOOTING GUIDE
In most cases, if the Solu Cube communicates with a
Master device at all, it will communicate correctly. If the
Solu Cube does not communicate at all, however,
review the following items:
Check Solu Cube
o Solu Cube is in Modbus mode
o Baud Rate and Parity are the same for Solu Cube
and Master device
o Instrument Address is correct
o If an option card was just installed, check to make
sure that the pins of the card are all fitted properly
into their respective sockets.
o If there may be a large common-mode voltage
between the Master and the Solu Cube, removing
the Earth Ground jumper on the Isolated Option
Card may improve communications.
Check Master
o Communications Port is working
If a breakout box or other communications indicators
are not available, use a voltmeter.
EIA232: connect a voltmeter between Master Tx and
Ground.
EIA485: connect a voltmeter between D+ and D-.
Voltage range should be 2VDC or 20VDC. Set the
Communications Port to the lowest baud rate. The
voltage should change when the Master transmits.
o Baud Rate and Parity are the same for Solu Cube
and Master device
o Instrument Address is correct
Check Connection between Master and Solu Cube
o EIA232: Solu Cube Receive to Master Transmit
Solu Cube Transmit to Master Receive
Ground to Ground
o EIA485: Solu Cube D+ to Master D+ or “A”
Solu Cube D- to Master D- or “B”
o All Transmit and Receive indicators should be off
while the connection is idle. If an indicator is con-
stantly on, there is a problem with the connection.
Notes
1. Typical Communication Port Pinouts
EIA485 Tx+ Tx- Rx+ Rx-
DB25 12 24 13 25
EIA232 Tx Rx Gnd
DB25 2 3 7
DB9 3 2 5
Some EIA232 communication software will work only if
handshaking signals seem to be active. This can be
simulated by connecting RTS to CTS (Request To Send
to Clear To Send) and connecting DTR to DSR (Data
Terminal Ready to Data Send Ready).
EIA232 RTS CTS DTR D S R
DB25
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