NXP Semiconductors LPC24XX UM10237 - Manual (Page 489)

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User manual Rev. 04 — 26 August 2009 489 of 792
NXP Semiconductors
UM10237
Chapter 18: LPC24XX CAN controllers CAN1/2
[1] If the CPU tries to write to this Transmit Buffer when the Transmit Buffer Status bit is '0' (locked), the written byte is not accepted and is
lost without this being signalled.
[2] The Transmission Complete Status bit is set '0' (incomplete) whenever the Transmission Request bit or the Self Reception Request bit
is set '1' for this TX buffer. The Transmission Complete Status bit remains '0' until a message is transmitted successfully.
8.9 Receive Frame Status Register (CAN1RFS - 0xE004 4020, CAN2RFS -
0xE004 8020)
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 CANxMOD is 1.
22 ES Error Status. This bit is identical to the ES bit in the CANxGSR. 0 0
23 BS Bus Status. This bit is identical to the BS bit in the CANxGSR. 0 0
31:24 - Reserved, user software should not write ones to reserved bits. The value
read from a reserved bit is not defined. NA
Table 427. Status Register (CAN1SR - address 0xE004 401C, CAN2SR - address 0xE004 801C) bit description
Bit Symbol Value Function Reset
Value RM
Set
Table 428. Receive Frame Status register (CAN1RFS - address 0xE004 4020, CAN2RFS -
address 0xE004 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
18–18 “Examples of acceptance filter tables and ID index values”
on page 518
for examples of ID Index values.
0 X
10 BP If this bit is 1, the current message was received in AF Bypass
mode, and the ID Index field (above) is meaningless. 0 X
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.
0 X
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. 0 X
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. 0 X