Espressif ESP32 Technical Reference Manual page 562

21 Two-wire Automotive Interface (TWAI)
21.5.4.3 Frame Identifier
The Frame Identifier fields is 2 bytes (11-bits) if the message is SFF, and 4 bytes (29-bits) if the message is
EFF.
The Frame Identifier fields for an SFF (11-bits) message is shown in Table 21-10-21-11.
Bit 31-8 Bit 7
Reserved ID.28
Bit 31-8 Bit 7
Reserved ID.20
The Frame Identifier fields for an EFF (29-bits) message is shown in Table 21-12-21-15.
Bit 31-8 Bit 7
Reserved ID.28
Bit 31-8 Bit 7
Reserved ID.20
Bit 31-8 Bit 7
Reserved ID.12
Bit 31-8 Bit 7
Reserved ID.4
21.5.4.4 Frame Data
The Frame Data fields contains the payload of transmitted or received a Data Frame, and can range from 0 to 8
bytes. The number of valid bytes should be equal to the DLC. However, if the DLC is larger than 8, the number
of valid bytes would still be limited to 8. Remote Frames do not have data payloads, thus the Frame Data fields
will be unused.
For example, when transmitting a Data Frame with 5 data bytes, the CPU should write a value of 5 to the DLC
field, and then fill in data bytes 1 to 5 in the Frame Data fields. Likewise, when receiving a Data Frame with a DLC
Espressif Systems
Table 21-10. TX/RX Identifier 1 (SFF); TWAI Address 0x44
Bit 6 Bit 5
ID.27 ID.26
Table 21-11. TX/RX Identifier 2 (SFF); TWAI Address 0x48
Bit 6 Bit 5
ID.19 ID.18
Table 21-12. TX/RX Identifier 1 (EFF); TWAI Address 0x44
Bit 6 Bit 5
ID.27 ID.26
Table 21-13. TX/RX Identifier 2 (EFF); TWAI Address 0x48
Bit 6 Bit 5
ID.19 ID.18
Table 21-14. TX/RX Identifier 3 (EFF); TWAI Address 0x4c
Bit 6 Bit 5
ID.11 ID.10
Table 21-15. TX/RX Identifier 4 (EFF); TWAI Address 0x50
Bit 6 Bit 5
ID.3 ID.2
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Bit 4 Bit 3 Bit 2
ID.25 ID.24 ID.23
Bit 4 Bit 3 Bit 2
1 2
X X X
Bit 4 Bit 3 Bit 2
ID.25 ID.24 ID.23
Bit 4 Bit 3 Bit 2
ID.17 ID.16 ID.15
Bit 4 Bit 3 Bit 2
ID.9 ID.8 ID.7
Bit 4 Bit 3 Bit 2
ID.1 ID.0 X
562
Bit 1 Bit 0
ID.22 ID.21
Bit 1 Bit 0
2 2 2
X X
Bit 1 Bit 0
ID.22 ID.21
Bit 1 Bit 0
ID.14 ID.13
Bit 1 Bit 0
ID.6 ID.5
Bit 1 Bit 0
1 2 2
X X
ESP32 TRM (Version 5.2)