REXGEN XML reference: CAN interfaces and bit timing

Set up each CAN port: its physical channel, bit rates, listen-only mode, sleep and wake behaviour and optional custom bit timing.

One block per CAN port

Add one CANINTERFACE to CANINTERFACE_LIST for every CAN port you use. Messages reach the port by naming the interface's UID in their InterfaceUID. Each block takes a UID attribute (required and unique in the file) and the optional Version, X and Y. Each entry in the settings lists gives the meaning, then whether the schema requires the element, its type and its default where one exists.

Only one interface can use each physical number.

CAN ports (CANINTERFACE_LIST)

CANINTERFACE

This port, from the example files, runs CAN 0 at 500 kbit/s with automatic bit timing, acknowledges frames and never sleeps.

<CANINTERFACE UID="4">
  <Type>CAN</Type>
  <PhysicalNumber>0</PhysicalNumber>
  <CANBusSpeed>500000</CANBusSpeed>
  <CANFDBusSpeed>8000000</CANFDBusSpeed>
  <CANFDNonISO>false</CANFDNonISO>
  <TSeg1>0</TSeg1>
  <TSeg2>0</TSeg2>
  <SJW>0</SJW>
  <TSeg1FD>0</TSeg1FD>
  <TSeg2FD>0</TSeg2FD>
  <SJWFD>0</SJWFD>
  <SilentMode>false</SilentMode>
  <Autodetect>false</Autodetect>
  <WakeUpOption>NO_WAKE_UP</WakeUpOption>
  <SleepOption>NO_SLEEP</SleepOption>
  <SleepNoActivityTime>0</SleepNoActivityTime>
  <Prescaler>0</Prescaler>
  <PrescalerFD>0</PrescalerFD>
  <UseBitTiming>false</UseBitTiming>
  <FilterCount>0</FilterCount>
</CANINTERFACE>

For a CAN FD bus, set Type to CAN_FD and CANFDBusSpeed to the data-phase bit rate, for example 2000000.

Type

The protocol: CAN (classic CAN 2.0) or CAN_FD. REXGEN 1 supports CAN only. Required.

PhysicalNumber

The physical channel on the logger, counted from 0. The PhysicalNumber table lists the valid values for each model. Required. Unsigned byte.

CANBusSpeed

Classic CAN bit rate, or the arbitration-phase bit rate on CAN FD, in bit/s from 0 to 1,000,000. For example 500000. Required. Unsigned int.

CANFDBusSpeed

CAN FD data-phase bit rate in bit/s from 0 to 8,000,000. The logger applies it only when Type is CAN_FD. The example files leave 8000000 in classic interfaces. Required. Unsigned int.

CANFDNonISO

true for a non-ISO (Bosch) CAN FD bus, false for ISO CAN FD and for classic CAN. Required. Boolean.

SilentMode

true puts the port in listen-only mode: it neither acknowledges frames nor transmits. Use it on a bus where the logger must stay invisible. Required. Boolean. Normally false.

Autodetect

true makes the logger detect the bit rate itself. Detection needs traffic on the bus. Required. Boolean.

WakeUpOption

WAKE_UP lets traffic on this port wake the logger. NO_WAKE_UP does not. Required. Default NO_WAKE_UP.

SleepOption

Sleep behaviour for this port: NO_SLEEP, NORMAL_SLEEP or DEEP_SLEEP. Required. Default NO_SLEEP.

SleepNoActivityTime

Seconds without bus activity before the logger sleeps, when SleepOption allows sleep. Required. Unsigned short.

UseBitTiming

true applies your own prescaler, segment and SJW values instead of timing worked out from the bit rates. Required. Boolean. Normally false.

Prescaler, TSeg1, TSeg2, SJW

Classic or arbitration-phase bit timing, used only when UseBitTiming is true. Required. Unsigned byte each. 0 when unused.

PrescalerFD, TSeg1FD, TSeg2FD, SJWFD

CAN FD data-phase bit timing, used only when UseBitTiming is true. Required. Unsigned byte each. 0 when unused.

FilterCount

Number of hardware acceptance filters. Optional. Unsigned short. Default 0.

HW_FILTER_LIST

Hardware acceptance filters. Each is a HW_FILTER with FilterType (RANGE, DUAL or CLASSIC), ID1, ID2, Extended and Accept. The example files filter with the identifier ranges on CANMESSAGE instead. Optional.

Custom bit timing

With UseBitTiming at false, the logger works out the timing from CANBusSpeed and CANFDBusSpeed. Set your own values only when a bus needs a specific sample point that the default does not give.

Each bit is divided into time quanta: one synchronisation quantum, then TSeg1, then TSeg2. The bus samples the bit between the two segments. SJW limits how far the controller can stretch or shorten a segment to stay in step.

• Bit rate = CAN clock / (Prescaler × (1 + TSeg1 + TSeg2))
• Sample point = (1 + TSeg1) / (1 + TSeg1 + TSeg2)

The data phase of CAN FD uses the same formulas with the FD values.

These Learn articles explain the theory:

• CAN bus baud rate and its calculation
• CAN versus CAN FD

CAN errors (CANERROR_LIST)

CANERROR

A CANERROR block attaches to one CAN interface.

<CANERROR UID="6">
  <InterfaceID>4</InterfaceID>
</CANERROR>

InterfaceID

UID of the CANINTERFACE it watches. Required. Unsigned short.

For what CAN error frames mean, see CAN errors explained.

Common mistakes

• Two interfaces with the same PhysicalNumber. Only one block can claim each channel.
• A PhysicalNumber the model does not have. The file still validates, but the port never comes up.
• Setting timing values while UseBitTiming is false. The logger ignores them until it is true.
• SilentMode set to true on a bus where the logger is the only other node. With nobody to acknowledge frames, the sender keeps repeating them.

Next: REXGEN XML reference: CAN messages and signals.