Espressif ESP32 Technical Reference Manual page 547

21 Two-wire Automotive Interface (TWAI)
The TWAI protocol has the following frame formats:
• Standard Frame Format (SFF) that consists of a 11-bit identifier
• Extended Frame Format (EFF) that consists of a 29-bit identifier
21.3.2.1 Data Frames and Remote Frames
Data Frames are used by nodes to send data to other nodes, and can have a payload of 0 to 8 data bytes.
Remote Frames are used to nodes to request a Data Frame with the same Identifier from another node, thus
does not contain any data bytes. However, Data Frames and Remote Frames share many common fields. Figure
21-1 illustrates the fields and sub fields of the different frames and formats.
Figure 21-1. The bit fields of Data Frames and Remote Frames
Arbitration Field
When two or more nodes transmits a Data or Remote Frame simultaneously, the Arbitration Field is used to de-
termine which node will win arbitration of the bus. During the Arbitration Field, if a node transmits a Recessive
bit but observes a Dominant bit, this indicates that another node has overridden its Recessive bit. Therefore,
the node transmitting the Recessive bit has lost arbitration of the bus and should immediately become a Re-
ceiver.
The Arbitration Field primarily consists of the Frame Identifier that is transmitted most significant bit first. Given
that a Dominant bit represents a logical 0, and a Recessive bit represents a logical 1:
Espressif Systems 547
Submit Documentation Feedback
ESP32 TRM (Version 5.2)