Datasheet

UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 306 of 547
NXP Semiconductors
UM10398
Chapter 16: LPC111x/LPC11Cxx C_CAN controller
The transmission of any number of Message Objects may be requested at the same time,
and they are transmitted subsequently according to their internal priority. Messages may
be updated or set to not valid any time, even when their requested transmission is still
pending. The old data will be discarded when a message is updated before its pending
transmission has started.
Depending on the configuration of the Message Object, the transmission of a message
may be requested autonomously by the reception of a remote frame with a matching
identifier.
16.7.2.3 Disabled Automatic Retransmission (DAR)
According to the CAN Specification (ISO11898, 6.3.3 Recovery Management), the CAN
controller provides means for automatic retransmission of frames that have lost arbitration
or that have been disturbed by errors during transmission. The frame transmission service
will not be confirmed to the user before the transmission is successfully completed. By
default, the automatic retransmission on lost arbitration or error is enabled. It can be
disabled to enable the CAN controller to work within a Time Triggered CAN (TTCAN, see
ISO11898-1) environment.
The Disable Automatic Retransmission mode is enabled by programming bit DAR in the
CAN Control Register to one. In this operation mode the programmer has to consider the
different behavior of bits TXRQST and NEWDAT in the Control Registers of the Message
Buffers:
• When a transmission starts, bit TXRQST of the respective Message Buffer is reset
while bit NEWDAT remains set.
• When the transmission completed successfully, bit NEWDAT is reset.
• When a transmission failed (lost arbitration or error), bit NEWDAT remains set. To
restart the transmission, the CPU has to set TXRQST back to one.
16.7.2.4 Test modes
The Test mode is entered by setting bit TEST in the CAN Control Register to one. In Test
mode the bits TX[1:0], TX0, LBACK, SILENT, and BASIC in the Test Register are writable.
Bit RX monitors the state of pin CAN_RXD and therefore is only readable. All Test register
functions are disabled when bit TEST is reset to zero.
16.7.2.4.1 Silent mode
The CAN core can be set in Silent mode by programming the Test register bit SILENT to
one.
In Silent Mode, the CAN controller is able to receive valid data frames and valid remote
frames, but it sends only recessive bits on the CAN bus, and it cannot start a
transmission. If the CAN Core is required to send a dominant bit (ACK bit, overload flag,
active error flag), the bit is rerouted internally so that the CAN Core monitors this dominant
bit, although the CAN bus may remain in recessive state. The Silent mode can be used to
analyze the traffic on a CAN bus without affecting it by the transmission of dominant bits
(Acknowledge Bits, Error Frames).