Functional Description

The following section describes the internal measurement and gives a detailed description of the interfaces.

2.1Current measurement

2.1.1Measurement procedure

The current is measured internally at a sampling rate of 1MS/s, where 8 samples are averaged to 1 internal sample. Thus, a “real” internal sampling rate of 125kS/s is achieved. This “real” internal sampling rate can be streamed to a PC via Ethernet. The internal sampling rate can be further reduced in the CMM-IV-GUI. Possible values are 125, 50, 10 and 1 kS/s.

The current range is selected automatically, when the CMM is switched on. Large current steps can result in short-time voltage drops of a few hundred millivolts across the module. See Dynamic behavior for dynamic behavior.

The CMM-IV transmits the average of the current for a configurable period via CAN. The standard value for this period is 5 ms.

Additionally, the average, the minimum and the maximum current can be read via CAN-Iso-TP. The calculation of the average, the minimum and the maximum value is reset with every readout. The following figure illustrates the averaging.

2.1.2Reverse current detection

Reverse currents cannot be measured, but a flag signals when a current of several 100mA is applied in reverse direction. The output data is set to zero if reverse current is detected. The flag can be read via IsoTP-protocol and the TCP-Streaming mode.

2.1.3Dynamic behavior

Switching between the ranges occurs very fast from low current range to high current ranges within less than 1µs (500ns typical) after the current range has been exceeded. This is significantly faster than the current can rise due to wiring inductance even with short wires.

The following figure shows the current (red) through the CMM and the voltage drop (yellow) across the CMM for a load current step from 0 to 100 A. The ringing on the voltage drop is caused by the wiring inductance.

2.2ON/Off control

CMM-IV may be switched on or off by a hardware input or by software. The following parameters can be adjusted by configuration:

• Active level (high or low) of the hardware input
• Priority of hardware or software on/off-control

Configuration may be changed in the CMM-IV-GUI, by the command OnOffMode = x via Text-Based Ethernet-Protocol or CAN using ISO-TP protocol, while x one of the following numbers 0…7:

2.3CAN data output

CAN data is sent cyclically on a specified CAN ID. This CAN ID is adjustable via text-based Ethernet-Protocol or CAN using ISO-TP protocol.

Content of the transmitted CAN message is as follows:

The CAN Message has a DLC (Data Length Code) of 8. Only Bytes 0 – 5 are used, Bytes 6 – 7 are padded with 0. Current is returned as 32 Bit unsigned long value in steps of 100nA split into the first 4 bytes of the CAN message. When CMM-IV is in off state, the returned value is zero. When CMM-IV is in on state, but reverse current is applied, the returned value is zero and “Negative Current Flag” (0x01) is set.

Flags:

• 0x01: Negative Current
• 0x02: Drop Voltage
• 0x04: Ringbuffer Warning
• 0x08: Cmm Off (0 = On; 1 = Off)

2.4Configuration tool CMM-IV-GUI

The tool CMM-IV-GUI can be used to configure a CMM-IV and can also trigger measurements or stream all measured values to a PC. The current version of the CMM-IV-GUI can be downloaded from:

myIRS – Downloads

After installation the installation folder contains (among others) the following subfolders and files:

2.4.1Connect and update a CMM-IV

The CMM-IV-GUI uses Ethernet and TCP/IP to communicate with the CMM-IV. Therefore, it is necessary to enter the IP-address of CMM-IV into the GUI. The default IP-address is 192.168.222.21. See Ethernet connection for details on IP configuration. If you do not know the IP-address of the CMM-IV, you can use Tools -> Detect module.

If “Detect module” does not find an IP address, make sure that the subnet mask of your network card is configured correctly and check your firewall settings.

After entering the IP address under “Remote IP” you can check the connection with “IDENTIFY”. This button opens a window which lists information about the connected CMM-IV. This information includes the serial number and the firmware version of the connected CMM-IV. If the firmware version is outdated, you can update the microcontroller under Tools -> Bootloader. The latest firmware version can be found with Help -> Check for update.

The bootloader is simple to use. Just enter the IP address of the CMM IV and click “START…”. Then select the firmware image from the installation folder mentioned above.

2.4.2Use the test panel to configure the CMM-IV and to get current measurements

The test panel can be opened by clicking “TESTPANEL” in the main window. It can be used to configure the different communication interfaces and the measurement behavior of the CMM-IV.

“ON/OFF CONTROL” can be used to select the modes described in ON/Off control.

There are three different methods of getting measurement values.

The first method simply uses the “READ” button. This immediately returns the requested number of current samples. With this method up to 100000 samples can be read. The maximum number of samples is reduced to 10000 if the maximum sample rate of 125 kS/s is used.

The second method is more advanced and uses the Buttons “INIT”, “SW TRIGGER” and “FETCH”. The button “INIT” sets the trigger method selected in the dropdown menu and the number of samples that shall be read. The number of samples for this method is limited to 100. The button “SW TRIGGER” must be used to trigger the measurement if trigger mode “Internal” is selected. In “External” trigger mode the measurement is triggered by a positive edge on the ON/OFF pin and in mode “Immediately“ no trigger is needed and measurement starts immediately after “INIT”. The button “FETCH” returns the configured number of current samples when the measurement is completed.

The third method uses the button “MINIMUM/MEAN/MAXIMUM”. A click on this button returns the minimum, mean and maximum current since the last use of this button.

The test panel offers two possibilities to configure the measurement behavior under “MISCELLANEOUS”.

“Minimum range” can be used to avoid undesired switching between ranges. The minimum range is reset to zero when rebooting the CMM-IV. A maximum range can not be set because it could easily lead to accidentally exceeding the maximum allowed current of the selected range.

“Sample rate” can be used to reduce the sample rate of the CMM IV. This could especially be helpful to reduce the size of the saved data, when using streaming of measurement values for longer time periods.

2.4.3Streaming of measured values

Streaming of measured values can be started in the main window of the CMM-IV-GUI. When “trigger disabled” is selected, streaming starts with a click on “START” and ends with a click on “STOP”. When “SW falling edge” or “SW rising edge” is selected, streaming starts but no data is saved until the selected edge is detected. The level for the edge detection can be configured under “SW trigger level [A]”. When an edge is detected 12500 samples before and 12500 samples after the edge are saved. With the default sample rate of 125 kS/s this results in 100 ms before and after the trigger event. In trigger mode “HW” a rising edge on the ON/OFF pin is used as trigger. After the click on “START” the microcontroller on the CMM-IV is set in a waiting mode and only starts streaming after the rising edge on pin ON/OFF is detected.

The streamed measurement data is saved in the proprietary “cmm4” format. This is a binary format which unloads the PC from data conversion and therefore allows streaming from multiple CMM-IV in parallel. The conversion to the TDMS format from National Instruments can be done from the menu (Tools -> Export to TDMS). To use the export function, you first need to install a TDMS library from National Instruments (Tools -> Install TDMS library).

“Export to TDMS” opens the dialogue window shown in Figure 10. In this window you can select the cmm4 file which should be converted to TDMS format. The TDMS file is saved with the same name as cmm4 file. The marked selection offers three possibilities. “CMM4 (current only)” exports only the measured current values. “CMM4 (all channels)” also includes the drop voltage, range and flags. “CMM4 (ignore trigger event)” exports all data from the click on “START” until the end of the cmm4 file which is 12500 samples after the trigger event. This is possible because all data is stored in the cmm4 file (including the trigger event) and the trigger is only used when exporting to TDMS.

2.4.4Live view of measured values

A click on “CHART” in the main window opens the window shown in Figure 11. The measured values are updated every second and displayed in the chart.

2.5Text-Based Ethernet-Protocol

The following sections describe the text-based Ethernet-protocol which is used by the CMM-IV-GUI and the C#-DLL. It is recommended to use the CMM-IV-GUI or the C#-DLL (which is part of the CMM-IV-GUI download package, see Configuration tool CMM-IV-GUI for details).

The protocol is based on TCP and uses 0-terminated strings. This means the last character of each command has to be NUL (= 0x00).

2.5.1Commands to measure currents, voltage drop and temperature of CMM IV

The text-based Ethernet protocol supports two different methods of reading currents. The first method is to simply use the ReadCurrent command with TriggerMode IMM. This immediately returns the requested number of current samples. The second method is more advanced and uses the commands InitCurrent, TriggerCurrent and FetchCurrent. InitCurrent sets the trigger method and the number of samples that shall be read. TriggerCurrent is used to trigger the measurement if trigger mode INT is selected. FetchCurrent returns the requested number of current samples when the measurement is completed.

The following commands can be sent as strings on TCP port 5025 and must be finished with the NUL-character (0x00). Erroneous commands are answered by an error message, see Error messages for details.

2.5.2Commands to query configuration parameters

The following commands can be sent as strings on TCP port 5025 and must be finished with the NUL-character (0x00). Erroneous commands are answered by an error message, see Error messages for details.

2.5.3Commands to set configuration parameters

The following commands can be sent as strings on TCP port 5025 and must be finished with the NUL-character (0x00). Erroneous commands are answered by an error message, see Error messages for details. If a command uses multiple parameters, the parameters must be separated by a whitespace. Optional parameters are noted in square brackets.

2.5.4Error messages

Erroneous commands are answered by one of the following strings (where it is appropriate, the error message contains the received string to simplify debugging):

• !Incorrect number of arguments: <received string>
• !This command is not supported: <received string>
• !This action is not supported: <received string>
• !Values out of range: <received string>
• !FRAM write failed.
• !No data available, maybe there was no trigger.
• !Error: <errorcode>
• !Waiting for reset to complete, commands are ignored.

2.6CAN configuration

Configuration of CMM may be performed using the CAN interface. For this configuration ISO-TP protocol is applied, according to ISO 15765-2. Normal addressing mode is used.

Configuration is performed by sending commands to CMM. Every command is acknowledged by a response.

By default, CMM IV uses the following IDs for ISO-TP:

• CMM IV listens on Local-ID (TPLID) for Commands: 0x1C3
• CMM IV sends Responses on Remote-ID (TPRID): 0x7FF

2.6.1ISO TP Header

Single frame commands

Most commands and responses fit into a single CAN message. I.e. single frames according to ISO-15765-2 may be used. The respective CAN message carries the following data:

Multiple frame commands

If more than one message is necessary for a command, first frames, flow-control and consecutive frames are used in the following order from top to bottom:

If the multiple frame message is a response, exchange the CAN-IDs TPRID and TPLID.

Data Byte 1/2 xx_N_PCI

Data byte 1 contains frame type and data length information according to ISO 15765-2.

For Single frames the values 0x04…0x07 are valid, which represent the number of following data bytes. 4 bytes minimum for Command, Action, Error-code, and Reserved - 7 bytes maximum including 3 command dependent data bytes.

For first frames 0x10 in byte 1 is added to the command length, which can be found in byte 2.

For consecutive frames 0x20 is added to a message counter in byte 1.

2.6.2Command Header

Data Byte 2/3 Command

Byte 2 for single frames, byte 3 for multiple frames

Data Byte 3/4 Action

Byte 3 for single frames, byte 4 for multiple frames

Data Byte 4/5 Error-code

Byte 4 for single frames, byte 5 for multiple frames. This data byte is only valid for responses from CMM. In commands to CMM this byte should always be 0x00 = No error.

Data Byte 5/6 Reserved

Byte 5 for single frames, byte 6 for multiple frames. This byte is reserved for future use.

2.6.3Command overview

The following commands are available:

Please note, that only command header and command dependent data is shown. ISO 15765 header must be added and messages have to be split into several messages, if necessary.

2.6.4Response overview

Every command is acknowledged by a response.

Most commands are executed first and a response is sent after execution. Exceptions from this rule are as follows:

• RESET:
  • The response is sent immediately.
  • Reset is performed afterwards.
  • Reboot of CMM IV may take up to 10 seconds
• TPLID, TPRID:
  • The response is sent with the previous CAN ID.
  • Respective CAN ID for ISO-TP is changed after the response has been sent.
• CANBD:
  • Baud rate is changed after response has been sent.
  • Please note that bus errors may occur after baud rate has been changed. CMM should be restarted afterwards.

Negative Responses

Negative responses are returned when a failure has occurred. I.e. the command was invalid and has been rejected.

Positive Responses

Positive responses to the respective commands are as follows. Please note that only command header and command dependent data is shown. ISO-TP header must be added and messages have to be split into several messages, if necessary.

2.6.5Example CAN traces

The following CAN traces should help understand the tables above. The command and responses are marked in the last column: Command / Response. Please note, that flow control frames are integrated in the respective command or response, but they are sent by the respective counterpart.

CMMON: switch ON

CMMON: switch OFF

SWVER (Read SW Version)

SINTV (set serial interval)