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UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
1095 of 1269
NXP Semiconductors
UM10503
Chapter 42: LPC43xx C_CAN
42.7.2.4.2
Loop-back mode
The CAN Core can be set in Loop-back mode by programming the Test Register bit
LBACK to one. In Loop-back Mode, the CAN Core treats its own transmitted messages as
received messages and stores them (if they pass acceptance filtering) into a Receive
Buffer.
This mode is provided for self-test functions. To be independent from external stimulation,
the CAN Core ignores acknowledge errors (recessive bit sampled in the acknowledge slot
of a data/remote frame) in Loop-back mode. In this mode the CAN core performs an
internal feedback from its CAN_TD output to its CAN_RD input. The actual value of the
CAN_RD input pin is disregarded by the CAN Core. The transmitted messages can be
monitored at the CAN_TD pin.
42.7.2.4.3
Loop-back mode combined with Silent mode
It is also possible to combine Loop-back mode and Silent mode by programming bits
LBACK and SILENT to one at the same time. This mode can be used for a “Hot Self test”,
meaning the C_CAN can be tested without affecting a running CAN system connected to
the pins CAN_TD and CAN_RD. In this mode the CAN_RD pin is disconnected from the
CAN Core and the CAN_TD pin is held recessive.
Fig 152. CAN core in Silent mode
CAN CORE
TD
RD
C_CAN
= 1
Rx
Tx
Fig 153. CAN core in Loop-back mode
CAN CORE
TD
RD
C_CAN
Rx
Tx