Functional Description

The following section describes the functionality of the internal measurement and every interface.

2.1Current measurement

2.1.1Measurement procedure

The current is measured internally at a sampling rate of 375kS/s, where 9 samples are averaged to 1 “external” sample. Thus, an “external” sampling rate of 41,667kS/s is achieved.

The current range is selected automatically, when CMM is switched on. Range selection does not influence the output voltage. Except large current changes of several amperes will result in short time voltage drops of few 100 mV. See Dynamic behavior for dynamic behavior.

For every interface (RS232, CAN, LVDS-SPI) an independent averaging is implemented, which starts averaging with every readout. Following figure illustrates the averaging.

I.e. if CAN sends its message every millisecond, around 42 external samples are averaged, which are already an average of 9 internal samples each.

Averaging from readout to readout does not influence the averaging on other interfaces. I.e., averaging is independent for

• RS232
• CAN
• LVDS-SPI

An overflow of the averaging may not occur even after a year of readout interval.

2.1.2Reverse current detection

Reverse currents can’t be measured, but a flag is signaled, when a current of several 100mA is applied in reverse direction. The output data on CAN or LVDS-SPI is an invalid number, exceeding the measurement range (0xEEEEEEEE in hexadecimal representation).

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.

The following figure shows the typical behavior at a current step from some µA to more than 60 amps.

• yellow trace: current through the module
• Red trace: voltage drop over the module

The ring at the voltage drop results from the inductive component of the applied load.

The following figure shows the zoom of positive and negative edge of the current step.

Conclusion: The voltage drop while switching occurs is well below 1V for a duration of some microseconds maximum.

2.2ON/Off control

CMM_III 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 by the command ONMOD=x via RS232 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 by RS232 configuration.

Content of the transmitted CAN message is as follows:

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_III is in off state, the returned value is 0xFFFFFFFF, which represents 429.4967295 A, which is no valid measurement value.

When CMM_III is in on state, but reverse current is applied, the returned value is 0xEEEEEEEE, which represents 400.8636142 A, which is no valid measurement value.

2.4LVDS-SPI data output

The measurement value can be read via an SPI-interface on LVDS level. SPI yields high data rates, while LVDS level yields low noise radiation and higher noise immunity, due to differential signaling.

The protocol for reading data of a single current measurement module is as follows:

When several modules are connected in daisy chain, the data from the previous module is forwarded to the output as following figure illustrates:

When En_In is asserted, the module sends out its current value during the next 32 clock cycles with MSB first. After 32 clock cycles the received data word is forwarded. En_In must be valid for 32 clock cycles, multiplied by number of CMMs in the chain. The current is returned as 32 Bit unsigned long value in steps of 100nA.

2.5RS232 data output

The measurement value is sent over RS232 in the interval of 100ms. The interval is adjustable via RS232 configuration. Connect the PC’s COM-Port to the RS232 at the front cover with a simple 1:1 Sub-D-Cable (no Null modem). Use a standard terminal program with the following settings:

• 9600 Baud
• No parity
• 1 Stop bit
• No Handshake

You will see the module’s output as following picture illustrates:

• R = Range
• I = average current in µA since last readout
• Min = minimum current in µA since last readout
• Max = maximum current in µA since last readout

Every Line is terminated by “Carriage Return / Line feed” to separate between new data.

2.6RS232 configuration

Configuration of the module using RS232 gives access to the CAN transmission configuration and the send interval for RS232-interface data output. Connect the PC’s COM-Port to the RS232 at the front cover with a simple 1:1 Sub-D-Cable (no Null modem).

Use a standard terminal software with the settings:

• 9600 Baud
• No parity
• 1 Stop bit
• No Handshake

You will see the module’s output as shown in RS232 data output.

By sending the commands of the following table the settings may be queried. Every Command must be finished with a carriage return / line feed (\r\n). I.e. every command string needs to have the following format similar to the following example: SINTV?\r\n

• \r is ASCII character 0x0D
• \n is ASCII character 0x0A

By sending the commands of the following table the settings may be set. Every Command must be finished with a carriage return / line feed (\n\r). I.e., every command string needs to have the following format like the following example: SINTV=100\n\r

Furthermore, the following additional commands using RS232 are defined. The commands also must be finished with \r\n.

2.7CAN 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.

2.7.1ISO 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 depending 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.

2.7.2Command 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.

2.7.3Command overview

Following commands are available:

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

2.7.4Response overview

Every command is acknowledged by a response.

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

• RESET:
  • The response is sent immediately.
  • Reset is performed afterwards.
• 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 changed. CMM should be restarted afterwards.

Negative Responses

Negative responses are returned when a failure 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.

Command dependent data of the GLVAL response:

2.7.5Example CAN traces

The following CAN traces should help to understand the tables above. The command and responses are marked in the respective colors: 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)