CAN Controllers and Acceptance Filter 199 May 03, 2004
Philips Semiconductors Preliminary User Manual
LPC2119/2129/2292/2294ARM-based Microcontroller
Rx Frame Status Register (CANRFS - 0xE00x x020)
This register defines the characteristics 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. See Table 124 for details on specific CAN channel register address.
Rx Identifier Register (CANRID - 0xE00x x024)
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
124 for details on specific CAN channel register address.
Table 133: CAN Rx Frame Status Register (CANRFS - 0xE00x x020)
CANRFS Name 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 the section “Examples of Acceptance Filter Tables and ID Index
Values“ on page 209 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
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 bytes 1000-1111 = 8 bytes
With RTR=1, this value indicates the number of data bytes requested to be sent
back, with the same encoding.
0X
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 134: CAN Rx Identifier Register when FF=0 (CANRID - 0xE00x x024)
CANRID Name 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
Table 135: CAN Rx Identifier Register when FF=1 (CANRID - 0xE00x x024)
CANRID Name Function Reset Value RM Set
28:0 ID
The 29-bit Identifier field of the current received message. In CAN 2.0B these bits
are called ID29-0.
0X
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