SPRUI30H November 2015 – May 2024 DRA745 , DRA746 , DRA750 , DRA756
According to the CAN specification, the bit time is divided into four segments (see Figure 24-174):
Each segment consists of a specific number of time quanta. The length of one time quantum (tq), which is the basic time unit of the bit time, is given by the FCLK and the baud rate prescalers (BRPE and BRP). With these two baud rate prescalers combined, divider values from 1 to 1024 can be programmed:
tq = Baud Rate Prescaler / FCLK
Apart from the fixed length of the synchronization segment, these numbers are programmable. Table 24-744 describes the minimum programmable ranges required by the CAN protocol.
A given bit rate may be met by different bit time configurations.
Parameter | Range | Remark |
---|---|---|
Sync_Seg | 1 tq (fixed) | Synchronization of bus input to FCLK |
Prop_Seg | [1 … 8] tq | Compensates for the physical delay times |
Phase_Seg1 | [1 … 8] tq | May be lengthened temporarily by synchronization |
Phase_Seg2 | [1 … 8] tq | May be shortened temporarily by synchronization |
Synchronization Jump Width (SJW) | [1 … 4] tq | May not be longer than either Phase Buffer Segment |
For proper functionality of the CAN network, the physical delay times and the oscillator’s tolerance range have to be considered.