Modbus RTU RS-485
33
SFIDK.PS.023.D2.02
APPENDIX E & F
The Modbus module uses the following Modbus exception codes, when responding to a master
module:
Exception code (Dec) Exception name
01 Illegal function
02 Illegal data address
03 Illegal data value
04 Slave device failure
06 Device busy
APPENDIX E
Exception codes
If an exception code 04 is received, further requests have to be done to narrow down the exact
problem.
If any doubts about the address that failed, „Last Coil/HoldReg ErrorAddr“ can be read. This will
return the faulty address.
Modbus Modbus No. of Data Read/
register address bytes type
Description
write
4:00681 680 2 Word Last Coil ErrorAddr
(Modbus cmd: 1 or 5) R
4:00682 681 2 Word Last Coil ErrorNo
(127 = No error) R
4:00683 682 2 Word Last HoldReg ErrorAddr
(Modbus cmd: 3 or 16) R
4:00684 683 2 Word Last HoldReg ErrorNo
(127 = No error) R
Reading „Last Coil/HoldReg ErrorNo“ will return a detailed error reason. A list of error numbers
can be seen below.
Error Error
Number Number Error name Reason
(Dec) (Hex)
3 3 Write access denied This parameter is in a state where it is
not writable
4 4 Max. limit The value was greater than the allowed
maximum value
5 5 Min. limit The value was less than the allowed
minimum value
127 7F No error No problem
APPENDIX F
Run Indicator
The Run Indicator indicates the state of the device. Two states are possible: ON (0xFF) and OFF
(0x00). The device will be in state ON, unless a serious error is present.
The following errors can turn the state to OFF:
• When a
„Fatal Error“
is active on the
„Error Pending List“
• Boot up problems when powering up the flowmeter.
• If no measurement are delivered or the time between them is too high.
The last condition will be based on the following:
Only the internally broadcasted
flow-value is checked. The expected broadcast-rate is read at
power up. If a broadcast is not received after 10 times the expected broadcast rate, the broadcast
rate is re-read from the USM (it may have been changed since power up). If the broadcast rate
was not changed (and the rate was not zero), the Run Indicator is set OFF. Reception of ten
broadcasted (flow-) values within 10 times the expected window will set the run-indicator TRUE
again.
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