CAN Bus Workshop_Version 03__06-2008_EN.pdf - 第74页

1 - 12 S tudent Gu ide CAN BUS Wor kshop 3 CAN BU S Editio n 06/200 8 12 19 D at um 06 /2008 Ver s io n 0 3 C AN Bu s W o r k sh op Mat hia s M ic hel SIPL ACE Cam p us A utom ati o n and Driv e s 3. M es sung der Spannu…

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Student Guide CAN BUS Workshop
Edition 06/2008 3 CAN BUS
11
17Datum06/2008 Version 03 CAN Bus Workshop Mathias Michel
SIPLACE Campus
Automation and Drives
Terminating Resistors 40 Ohm
CAN High - Level < 1,5 V
CAN Low – Level < 1,5 V
3. Effect wrong terminating resistors
3. Auswirkung falscher Abschlußwiderstände
18Datum06/2008 Version 03 CAN Bus Workshop Mathias Michel
SIPLACE Campus
Automation and Drives
2. Check the Power fail, CAN init, -reset signals
Although the CAN Init and CAN Reset signals are not used in some cases (machine-specific),
they still have a voltage level of 5V (min.4,0V)
The sporadic drop in voltage or a short circuit to other signals could lead to logical faults in the
CAN bus system (e.g. CAN timeout).
Should problems with the CAN bus occur, always check the signal voltage levels
Note:
In some machines, the wires for CAN init,CAN reset and power fail may have been removed
from the CAN bus cable at the COM assembly. In this case, the easiest way to check
voltages levels is at the RS232 bridge, in the main and sub distributors.
3. Überprüfung der Spannungen
(CAN init,-reset,Power fail)
3. Checking the Power Fail, CAN Init,-Reset
Signals
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Student Guide CAN BUS Workshop
3 CAN BUS Edition 06/2008
12
19Datum06/2008 Version 03 CAN Bus Workshop Mathias Michel
SIPLACE Campus
Automation and Drives
3. Messung der Spannungspegel
3. Check the recessive level
The CAN levels for CAN_H and CAN_ L differentiate between recessive and dominant levels.
This two levels will convert into a TTL level, for the CAN Processor. The RxD Signal has the
same phase such as the CAN_L Signal.
3. Checking the CAN BUS voltage
level
CAN_L
CAN_H
RxD
TTL Pegel
(Level)
16bit Can
processor
TQM
module
RxD
Naming convention for the CAN Signals
CAN_H : Recessive Signal (r)
Logic 1 (1)
High (H)
CAN_L: dominate Signal (d)
Logic 0 (0)
Low (L)
20Datum06/2008 Version 03 CAN Bus Workshop Mathias Michel
SIPLACE Campus
Automation and Drives
3. Messung der Spannungspegel
3. Check the recessive level
The recessive level (when CAN bus is idle i.e. there is no data transmission) can be measured statically,
with a voltammeter. Make sure no telegrams are sent during the measurement procedure. This means that
measurement may only be performed when the machine is not in operation.
Recessive Pegel = Logic „1“
Attention: Switch ON the machine and wait, so that are no communication on the CAN Bus!
Measure between GND and Pin 3 and GND and Pin 6).
Voltage value: 2.5 +/- 0,3V for CAN_H
2.5 +/-0,3V for CAN_L
3. Checking the CAN BUS voltage
level
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Student Guide CAN BUS Workshop
Edition 06/2008 3 CAN BUS
13
21Datum06/2008 Version 03 CAN Bus Worksh op Mathias Michel
SIPLACE Campus
Automation and Drives
3. Messung der Spannungspegel
4. Check the dominant level
Dominant Level = Logic „0“
You need an oscilloscope to measure the dominant level.
To minimize the extent to which the measurement system influences the CAN signals, keep the
measurement line as short as possible.
- Connect the CAN Test Box to the service plug of the COM unit.
- Connect the oscilloscope to the BNC connectors CAN_H and CAN_L.
- Switch ON the machine
- To simulate CAN bus communication, you can start a version query in Sitest or Caccia.
- You can now check the signal voltage levels on the oscilloscope.
You should receive a value of 3.5V ( 2.75 - 4.5V) for CAN_H and of 1.5V (2.0 - 1.0V) for CAN_L
Voltage value:
CAN_H 3.5V ( 2.75 – 4.5V);
CAN_L 1.5V (2.0 – 1.0V)
3. Checking the CAN BUS voltage
level
22Datum06/2008 Version 03 CAN Bus Workshop Mathias Michel
SIPLACE Campus
Automation and Drives
3. Beispiele für mögliche Fehlerquellen
Short circuit between CAN High – Signal and GND
CAN High - Level
CAN Low - Level
3. Example for CAN BUS Errors