NXP Semiconductors LPC24XX UM10237 - Manual (Page 493)

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User manual Rev. 04 — 26 August 2009 493 of 792
NXP Semiconductors
UM10237
Chapter 18: LPC24XX CAN controllers CAN1/2
8.14 Transmit Identifier Register (CAN1TID[1/2/3] - 0xE004 40[34/44/54],
CAN2TID[1/2/3] - 0xE004 80[34/44/54])
When the corresponding TBS bit in CANxSR is 1, software can write to one of these
registers to define the Identifier field of the next transmit message. Bits not listed read as 0
and should be written as 0. The register assumes two different formats depending on the
FF bit in CANTFI.
In Standard Frame Format messages, the CAN Identifier consists of 11 bits (ID.28 to
ID.18), and in Extended Frame Format messages, the CAN identifier consists of 29 bits
(ID.28 to ID.0). ID.28 is the most significant bit, and it is transmitted first on the bus during
the arbitration process. The Identifier acts as the message's name, used in a receiver for
acceptance filtering, and also determines the bus access priority during the arbitration
process.
8.15 Transmit Data Register A (CAN1TDA[1/2/3] - 0xE004 40[38/48/58],
CAN2TDA[1/2/3] - 0xE004 80[38/48/58])
When the corresponding TBS bit in CANSR is 1, software can write to one of these
registers to define the first 1 - 4 data bytes of the next transmit message. The Data Length
Code defines the number of transferred data bytes. The first bit transmitted is the most
significant bit of TX Data Byte 1.
Table 434. Transfer Identifier Register (CAN1TID[1/2/3] - address 0xE004 40[34/44/54],
CAN2TID[1/2/3] - address 0xE004 80[34/44/54]) bit description
Bit Symbol Function Reset
Value RM
Set
10:0 ID The 11 bit Identifier to be sent in the next transmit message. 0 X
31:11 - Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined. NA
Table 435. Transfer Identifier register when FF = 1
Bit Symbol Function Reset
Value RM
Set
28:0 ID The 29 bit Identifier to be sent in the next transmit message. 0 X
31:29 - Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined. NA
Table 436. Transmit Data Register A (CAN1TDA[1/2/3] - address 0xE004 40[38/48/58],
CAN2TDA[1/2/3] - address 0xE004 80[38/48/58]) bit description
Bit Symbol Function Reset
Value RM
Set
7:0 Data 1 If RTR = 0 and DLC
≥
0001 in the corresponding CANxTFI, this
byte is sent as the first Data byte of the next transmit message.
0 X
15;8 Data 2 If RTR = 0 and DLC
≥
0010 in the corresponding CANxTFI, this
byte is sent as the 2nd Data byte of the next transmit message.
0 X
23:16 Data 3 If RTR = 0 and DLC
≥
0011 in the corresponding CANxTFI, this
byte is sent as the 3rd Data byte of the next transmit message.
0 X
31:24 Data 4 If RTR = 0 and DLC
≥
0100 in the corresponding CANxTFI, this
byte is sent as the 4th Data byte of the next transmit message.
0 X