Espressif ESP32 Technical Reference Manual page 551

21 Two-wire Automotive Interface (TWAI)
21.3.2.3 Interframe Space
The Interframe Space acts as a separator between frames. Data Frames and Remote Frames must be separated
from preceding frames by an Interframe Space, regardless of the preceding frame's type (Data Frame, Remote
Frame, Error Frame, Overload Frame). However, Error Frames and Overload Frames do not need to be separated
from preceding frames.
Figure 21-4 shows the fields within an Interframe Space:
Interframe Space
Intermission
Suspend Transmission
Bus Idle
21.3.3 TWAI Errors
21.3.3.1 Error Types
Bus Errors in TWAI are categorized into one of the following types:
Bit Error
A Bit Error occurs when a node transmits a bit value (i.e., Dominant or Recessive) but the opposite bit is detected
(e.g., a Dominant bit is transmitted but a Recessive is detected). However, if the transmitted bit is Recessive
and is located in the Arbitration Field or ACK Slot or Passive Error Flag, then detecting a Dominant bit will not be
considered a Bit Error.
Stuff Error
A stuff error is detected when 6 consecutive bits of the same value are detected (thus violating the bit-stuffing
encoding).
CRC Error
A Receiver of a Data or Remote Frame will calculate a CRC based on the bits it has received. A CRC error occurs
when the CRC calculated by the Receiver does not match the CRC sequence in the received Data or Remote
Frame.
Form Error
A Form Error is detected when a fixed-form bit field of a message contains an illegal bit. For example, the r1 and
Espressif Systems
Figure 21-4. The Fields within an Interframe Space
Table 21-4. Interframe Space
Description
The Intermission consists of 3 Recessive bits.
An Error Passive node that has just transmitted a message must include
a Suspend Transmission field. This field consists of 8 Recessive bits.
Error Active nodes should not include this field.
The Bus Idle field is of arbitrary length. Bus Idle ends when an SOF is
transmitted. If a node has a pending transmission, the SOF should be
transmitted at the first bit following Intermission.
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ESP32 TRM (Version 5.2)