FlexCAN ModuleMCF5253 Reference Manual, Rev. 125-10 Freescale Semiconductor12LPBLoop back. Configures FlexCAN to operate in loop-back mode. In this mode, FlexCAN performs an internal loopback that can be used for self test operation. The bit stream output of the transmitter is fed back internally to thereceiver input. The Rx CAN input pin is ignored and the Tx CAN output goes to the recessive state (logic 1).FlexCAN behaves as it normally does when transmitting, and treats its own transmitted message as a messagereceived from a remote node. In this mode, FlexCAN ignores the bit sent during the ACK slot in the CAN frameacknowledge field, generating an internal acknowledge bit to ensure proper reception of its own message. Bothtransmit and receive interrupts are generated.0 Loop back disabled1 Loop back enabled11–8 Reserved, should be cleared.7SMPSampling mode. Determines whether the FlexCAN module will sample each received bit one time or three times todetermine its value.0 One sample, taken at the end of phase buffer segment 1, is used to determine the value of the received bit.1 Three samples are used to determine the value of the received bit. The samples are taken at the normal samplepoint and at the two preceding periods of the S-clock; a majority rule is used.6BOFFRECBus off recovery mode. Defines how FlexCAN recovers from bus off state. If this bit is cleared, automatic recoveringfrom bus off state occurs according to the CAN Specification 2.0B. If the bit is set, automatic recovering from busoff is disabled and the module remains in bus off state until the bit is cleared by the user. If the bit is cleared before128 sequences of 11 recessive bits are detected on the CAN bus, then bus off recovery happens as if theBOFFREC bit had never been set. If the bit is cleared after 128 sequences of 11 recessive bits occurred, thenFlexCAN will re-synchronize to the bus by waiting for 11 recessive bits before joining the bus. After clearing, theBOFFREC bit can be set again during bus off, but it will only be effective the next time the module enters bus off.If BOFFREC was cleared when the module entered bus off, setting it during bus off will not be effective for thecurrent bus off recovery.0 Automatic recovering from bus off state enabled, according to CAN Spec 2.0B1 Automatic recovering from bus off state disabled5TSYNTimer synchronize mode. Enables the mechanism that resets the free-running timer each time a message isreceived in Message Buffer 0. This feature provides the means to synchronize multiple FlexCAN stations with aspecial “SYNC” message (global network time).0 Timer synchronization disabled.1 Timer synchronization enabled.Note: There can be a bit clock skew of four to five counts between different FlexCAN modules that are using thisfeature on the same network.4LBUFLowest buffer transmitted first. Defines the ordering mechanism for message buffer transmission.0 Message buffer with lowest ID is transmitted first1 Lowest numbered buffer is transmitted first3LOMListen-only mode. Configures FlexCAN to operate in listen-only mode. In this mode transmission is disabled, allerror counters are frozen, and the module operates in a CAN error passive mode. Only messages acknowledgedby another CAN station will be received. If FlexCAN detects a message that has not been acknowledged, it will flaga BIT0 error (without changing the REC), as if it was trying to acknowledge the message.0 FlexCAN module is in normal active operation; listen-only mode is deactivated1 FlexCAN module is in listen-only mode operation2–0PROPSEGPropagation segment. Defines the length of the propagation segment in the bit time. The valid programmablevalues are 0–7.Note: A time-quantum = 1 S clock period.Table 25-3. FlexCAN Control (CANCTRLn) Register Field Descriptions (continued)Field DescriptionPropagation segment time (PROPSEG + 1) time-quanta=
