00194932-20 User Manual CAN Test Box-Error Frame Diagnostic unit_en.pdf - 第17页

1 - 17 Edition 10/2 018 SIPLACE CAN Bus 17 2.5 Checking the Power Fail, CAN Init, CAN Reset Sig- nals Note: Although the CAN Init and CAN Rese t signals are n ot used in som e cases (machin e-spe- cific), they still have…

1 - 16

SIPLACE CAN Bus Edition 10/2018

For the positions of the terminating resistors, refer to Chapter 1.9 CAN Bus Operation Diagrams.

1 - 17

Edition 10/2018 SIPLACE CAN Bus

2.5 Checking the Power Fail, CAN Init, CAN Reset Sig-

nals

Note: Although the CAN Init and CAN Reset signals are not used in some cases (machine-spe-

cific), they still have a voltage level of 5V. 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.

Step by step: 2

– Connect the CAN Test Box to the service plug (Note: Not all signals on the Service plug) of the

COM assembly.

– Switch the machine on.

– At the middle pin of the BNC socket, measure the CAN reset and power fail against ground,

for 5V DC voltage.

– The voltage level from the CAN init signal can be checked directly at the connector plug.

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.

2.5.1 Error Localization

Should CAN bus errors occur sporadically, it may be helpful to check the signals during the pro-

duction process.

Trigger the signals and use the CAN Test Box and an oscilloscope to monitor the 5V voltages.

This helps you to determine whether the signals are really stabile and ensures that no sporadic

drops in voltage occur.

You will need to find a temporary solution for checking the CAN init signal (e.g. solder a wire to the

RS 232 connector plug), as this is not available at the CAN Test Box.

1 - 18

SIPLACE CAN Bus Edition 10/2018

2.6 Checking the CAN Bus Voltage 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.

Abb. 2.6 - 1 RxD signal

2.6.1 Checking 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 proce-

dure. This means that measurement may only be performed when the machine is not in operation.

Step by step: 2

– Connect the CAN Test Box to the service plug (Note: Not all signals on the Service plug) of the

COM assembly.

– Switch the machine on and wait until it has booted.

– Measure the voltage level at the banana sockets between CAN H and GND or between CAN

L and GND, with the help of a measuring device.

– You should receive a voltage value of 2.5 V +/- 0.3 V for CAN_H and CAN_L.

Note: If you discover a short circuit or incorrect voltage level, disconnect the subsystems from

the CAN bus, one after the other. For suitable disconnection points, please refer to the circuit di-

agrams.

2.6.2 Checking the Dominant Level

The dominant CAN H and CAN L levels contain the information and need to reach a certain volt-

age level. These two CAN signals form a TTL CAN (RxD) signal, which can then be interpreted

by the CAN processor.

Note: 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 pos-

sible.

CAN_L

CAN_H

RxD

TTL Pegel

(Level)