Table of Contents
Advertisement
Chapter 1
Introduction
NI-CAN User Manual
Arbitration ID
The arbitration ID fields contain the identifier for a CAN frame. The
standard format has one 11-bit field, and the extended format has two
fields, which are 11 and 18 bits in length. In both formats, bits of the
arbitration ID are transmitted from high to low order.
Remote Transmit Request (RTR)
The Remote Transmit Request bit is dominant (0) for data frames, and
recessive (1) for remote frames. Data frames are the fundamental means of
data transfer on a CAN network, and are used to transmit data from one
device to one or more receivers. A device transmits a remote frame to
request transmission of a data frame for the given arbitration ID. The
remote frame is used to request data from its source device, rather than
waiting for the data source to transmit the data on its own.
Identifier Extension (IDE)
The Identifier Extension bit differentiates standard frames from extended
frames. Because the IDE bit is dominant (0) for standard frames and
recessive (1) for extended frames, standard frames are always higher
priority than extended frames.
Data Length Code (DLC)
The Data Length Code is a 4-bit field that indicates the number of data
bytes in a data frame. In a remote frame, the Data Length Code indicates
the number of data bytes in the requested data frame. Valid Data Length
Codes range from zero to eight.
Data Bytes
For data frames, this field contains from 0 to 8 data bytes. Remote CAN
frames always contain zero data bytes.
Cyclic Redundancy Check (CRC)
The 15-bit Cyclic Redundancy Check detects bit errors in frames. The
transmitter calculates the CRC based on the preceding bits of the frame,
and all receivers recalculate it for comparison. If the CRC calculated by a
receiver differs from the CRC in the frame, the receiver detects an error.
1-4
ni.com
Advertisement
Table of Contents
Troubleshooting
