UM10430 Datasheet, PDF (1110/1164 Pages) NXP Semiconductors – LPC18xx ARM Cortex-M3 microcontroller

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The NEWDAT bit is set to indicate that new data (not yet seen by the CPU) has been
received. The CPU/software should reset NEWDAT when it reads the Message Object. If
at the time of the reception the NEWDAT bit was already set, MSGLST is set to indicate
that the previous data (supposedly not seen by the CPU) is lost. If the RxIE bit is set, the
INTPND bit is also set, causing the Interrupt Register to point to this Message Object.
The TXRQST bit of this Message Object is reset to prevent the transmission of a Remote
Frame, while the requested Data Frame has just been received.
Reception of a remote frame: When a Remote Frame is received, three different
configurations of the matching Message Object have to be considered:
1. DIR = ‘1’ (direction = transmit), RMTEN = ‘1’, UMASK = ‘1’ or ’0’
On the reception of a matching Remote Frame, the TXRQST bit of this Message
Object is set. The rest of the Message Object remains unchanged.
2. DIR = ‘1’ (direction = transmit), RMTEN = ‘0’, UMASK = ’0’
On the reception of a matching Remote Frame, the TXRQST bit of this Message
Object remains unchanged; the Remote Frame is ignored.
3. DIR = ‘1’ (direction = transmit), RMTEN = ‘0’, UMASK = ’1’
On the reception of a matching Remote Frame, the TXRQST bit of this Message
Object is reset. The arbitration and control field (Identifier + IDE + RTR + DLC) from
the shift register is stored into the Message Object in the Message RAM, and the
NEWDAT bit of this Message Object is set. The data field of the Message Object
remains unchanged; the Remote Frame is treated similar to a received Data Frame.
42.10.7.3.5
Receive/transmit priority
The receive/transmit priority for the Message Objects is attached to the message number.
Message Object 1 has the highest priority, while Message Object 32 has the lowest
priority. If more than one transmission request is pending, they are serviced due to the
priority of the corresponding Message Object.
42.10.7.3.6 Configuration of a transmit object
Table 1046 shows how a transmit object should be initialized by software (see also
Table 1024):
Table 1046.Initialization of a transmit object
MSGVAL
Arbitration Data bits Mask bits
bits
1
application application application
dependent dependent dependent
EOB
1
DIR
NEWDAT
1
0
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User manual
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Rev. 00.13 — 20 July 2011
© NXP B.V. 2011. All rights reserved.
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