UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
1101 of 1269
NXP Semiconductors
UM10503
Chapter 42: LPC43xx C_CAN
The Arbitration Registers (ID28:0 and XTD bit) are given by the application. They define
the identifier and the type of the outgoing message. If an 11-bit Identifier (“Standard
Frame”) is used, it is programmed to ID28. In this case ID18, ID17 to ID0 can be
disregarded.
If the TXIE bit is set, the INTPND bit will be set after a successful transmission of the
Message Object.
If the RMTEN bit is set, a matching received Remote Frame will cause the TXRQST bit to
be set, and the Remote Frame will autonomously be answered by a Data Frame.
The Data Registers (DLC3:0, Data0:7) are given by the application. TXRQST and RMTEN
may not be set before the data is valid.
The Mask Registers (Msk28-0, UMASK, MXTD, and MDIR bits) may be used
(UMASK=’1’) to allow groups of Remote Frames with similar identifiers to set the TXRQST
bit. For details see
. The DIR bit should not be masked.
42.7.3.7 Updating a transmit object
The CPU may update the data bytes of a Transmit Object any time via the IFx Interface
registers. Neither MSGVAL nor TXRQST have to be reset before the update.
Even if only a part of the data bytes are to be updated, all four bytes of the corresponding
IFx Data A Register or IFx Data B Register have to be valid before the content of that
register is transferred to the Message Object. Either the CPU has to write all four bytes
into the IFx Data Register or the Message Object is transferred to the IFx Data Register
before the CPU writes the new data bytes.
When only the (eight) data bytes are updated, first 0x0087 is written to the Command
Mask Register. Then the number of the Message Object is written to the Command
Request Register, concurrently updating the data bytes and setting TXRQST.
To prevent the reset of TXRQST at the end of a transmission that may already be in
progress while the data is updated, NEWDAT has to be set together with TXRQST. For
details see
When NEWDAT is set together with TXRQST, NEWDAT will be reset as soon as the new
transmission has started.
42.7.3.8 Configuration of a receive object
shows how a receive object should be initialized by software (see also
Table 975. Initialization of a transmit object
MSGVAL
Arbitration
bits
Data bits
Mask bits
EOB
DIR
NEWDAT
1
application
dependent
application
dependent
application
dependent
1
1
0
MSGLST
RXIE
TXIE
INTPND
RMTEN
TXRQST
0
0
application
dependent
0
application
dependent
0