Datasheet

User manual Rev. 12.3 — 10 June 2014 307 of 547

NXP Semiconductors

UM10398

Chapter 16: LPC111x/LPC11Cxx C_CAN controller

16.7.2.4.2 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_TXD output to its CAN_RXD input. The actual value of the

CAN_RXD input pin is disregarded by the CAN Core. The transmitted messages can be

monitored at the CAN_TXD pin.

16.7.2.4.3 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 Selftest”,

meaning the C_CAN can be tested without affecting a running CAN system connected to

the pins CAN_TXD and CAN_RXD. In this mode the CAN_RXD pin is disconnected from

the CAN Core and the CAN_TXD pin is held recessive.

Fig 62. CAN core in Silent mode

CAN CORE

CAN_TXD CAN_RXD

C_CAN

= 1

Rx Tx

Fig 63. CAN core in Loop-back mode

CAN CORE

CAN_TXD CAN_RXD

C_CAN

Rx Tx