UM10360 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2013. All rights reserved.
User manual Rev. 3 — 19 December 2013 366 of 841
NXP Semiconductors
UM10360
Chapter 16: LPC176x/5x CAN1/2
16.7.9.1 ID index field
The ID Index is a 10-bit field in the Info Register that contains the table position of the ID
Look-up Table if the currently received message was accepted. The software can use this
index to simplify message transfers from the Receive Buffer into the Shared Message
Memory. Whenever bit 10 (BP) of the ID Index in the CANRFS register is 1, the current
CAN message was received in acceptance filter bypass mode.
16.7.10 CAN Receive Identifier register (CAN1RID - 0x4004 4024, CAN2RID -
0x4004 8024)
This register contains the Identifier field of the current received message. It is read-only in
normal operation but can be written for testing purposes if the RM bit in CANmod is 1. It
has two different formats depending on the FF bit in CANRFS. See Table 313
for details
on specific CAN channel register address.
Table 325. CAN Receive Frame Status register (CAN1RFS - address 0x4004 4020, CAN2RFS - address 0x4004 8020)
bit description
Bit Symbol Function Reset
Value
RM
Set
9:0 ID Index If the BP bit (below) is 0, this value is the zero-based number of the Lookup Table RAM entry
at which the Acceptance Filter matched the received Identifier. Disabled entries in the
Standard tables are included in this numbering, but will not be matched. See Section 16.17
“Examples of acceptance filter tables and ID index values” on page 394 for examples of ID
Index values.
0X
10 BP If this bit is 1, the current message was received in AF Bypass mode, and the ID Index field
(above) is meaningless.
0X
15:11 - Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
NA
19:16 DLC The field contains the Data Length Code (DLC) field of the current received message. When
RTR = 0, this is related to the number of data bytes available in the CANRDA and CANRDB
registers as follows:
0000-0111 = 0 to 7 bytes1000-1111 = 8 bytes
With RTR = 1, this value indicates the number of data bytes requested to be sent back, with
the same encoding.
0X
29:20 - Reserved, user software should not write ones to reserved bits. The value read from a
reserved bit is not defined.
NA
30 RTR This bit contains the Remote Transmission Request bit of the current received message. 0
indicates a Data Frame, in which (if DLC is non-zero) data can be read from the CANRDA
and possibly the CANRDB registers. 1 indicates a Remote frame, in which case the DLC
value identifies the number of data bytes requested to be sent using the same Identifier.
0X
31 FF A 0 in this bit indicates that the current received message included an 11-bit Identifier, while
a 1 indicates a 29-bit Identifier. This affects the contents of the CANid register described
below.
0X
Table 326. CAN Receive Identifier register (CAN1RID - address 0x4004 4024, CAN2RID - address 0x4004 8024) bit
description
Bit Symbol Function Reset Value RM Set
10:0 ID The 11-bit Identifier field of the current received message. In CAN 2.0A, these
bits are called ID10-0, while in CAN 2.0B they’re called ID29-18.
0X
31:11 - Reserved, user software should not write ones to reserved bits. The value read
from a reserved bit is not defined.
NA
To Next Page
Loading...
