759Chapter 18 AFCAN ControllerUser’s Manual U16580EE3V1UD0018.3.7 Baud rate control function(1) PrescalerThe CAN controller has a prescaler that divides the clock (fCAN ) supplied to CAN. This prescalergenerates a CAN protocol layer basic system clock (f TQ) derived from the CAN module systemclock (fCANMOD), and divided by 1 to 256 (“CnBRP - CANn module bit rate prescaler register” onpage 791).(2) Data bit time (8 to 25 time quanta)One data bit time is defined as shown in Figure 18-18: on page 759.The CAN Controller sets time segment 1, time segment 2, and re-Synchronization Jump Width(SJW) of data bit time, as shown in Figure 18-18 . Time segment 1 is equivalent to the total of thepropagation (prop) segment and phase segment 1 that are defined by the CAN protocol specifica-tion. Time segment 2 is equivalent to phase segment 2.Figure 18-18: Segment settingNotes: 1. IPT: Information Processing Time2. TQ: Time QuantaReference: The CAN protocol specification defines the segments constituting the data bit time asshown in Figure18-19.Table 18-15: Segment settingSegment name Settable range Notes on setting to conform to CAN specificationTime segment 1 (TSEG1) 2TQ to 15TQ -Time segment 2 (TSEG2) 1TQ to 8TQ IPT of the CAN controller is 0TQ. To conform to theCAN protocol specification, therefore, a length lessor equal to phase segment 1 must be set here.This means that the length of time segment 1minus 1TQ is the settable upper limit of timesegment 2.Re-synchronization JumpWidth (SJW)1TQ to 4TQ The length of time segment 1 minus 1TQ or 4 TQ,whichever is smaller.Data bit time(DBT)Phase segment 1Prop segmentSync segment Phase segment 2Time segment 1(TSEG1) Time segment 2(TSEG2)Sample point (SPT)
