38.7.7 Nominal Bit Timing and Prescaler
This register is write-restricted and writable only if both CCCR.CCE bit (CCCR <1>) and CCCR.INIT bit (CCCR <0>) are set.
The CAN bit time may be programmed in the range of 4 to 385 time quanta. The CAN time quantum may be programmed in the range of 1 to 512 GCLK_CANx periods. tq = (NBRP + 1) mtq.
Therefore the length of the bit time is [NTSEG1 + NTSEG2 + 3] tq, where NTSEG1 and NTSEG2 are programmed values in the NBTP register.
Note: With a CAN clock (GCLK_CANx) of
8MHz, the reset value 0x06000A03 configures the CAN for a bit rate of 500
kBits/s.
| Symbol | Description | Symbol | Description | Symbol | Description |
|---|---|---|---|---|---|
| R | Readable bit | HC | Cleared by Hardware | (Grey cell) | Unimplemented |
| W | Writable bit | HS | Set by Hardware | X | Bit is unknown at Reset |
| K | Write to clear | S | Software settable bit | — | — |
| Name: | NBTP |
| Offset: | 0x1C |
| Reset: | 0x00000A33 |
| Property: | Write-restricted |
| Bit | 31 | 30 | 29 | 28 | 27 | 26 | 25 | 24 | |
| NSJW[6:0] | NBRP[8] | ||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | |
| Bit | 23 | 22 | 21 | 20 | 19 | 18 | 17 | 16 | |
| NBRP[7:0] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| Bit | 15 | 14 | 13 | 12 | 11 | 10 | 9 | 8 | |
| NTSEG1[7:0] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | R/W | |
| Reset | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | |
| Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| NTSEG2[6:0] | |||||||||
| Access | R/W | R/W | R/W | R/W | R/W | R/W | R/W | ||
| Reset | 0 | 0 | 0 | 0 | 0 | 1 | 1 | ||
Bits 31:25 – NSJW[6:0] Nominal (Re)Syncronization Jump Width
| Value | Description |
|---|---|
| 0x00 - 0x7F | Valid values are 0 to 127. The actual interpretation by the hardware of this value is such that one more than the programmed value is used. |
Bits 24:16 – NBRP[8:0] Nominal Baud Rate Prescaler
| Value | Description |
|---|---|
| 0x000 - 0x1FF | The value by which the GCLK_CANx is divided for generating the bit time quanta. The bit time is built up from a multiple of this quanta. Valid values for the Baud Rate Prescaler are 0 to 511. The actual interpretation by the hardware of this value is such that one more than the value programmed here is used. |
Bits 15:8 – NTSEG1[7:0] Nominal Time segment before sample point
| Value | Description |
|---|---|
| 0x00 - 0x7F | Valid values are 1 to 255. The actual interpretation by the hardware of this value is such that one more than the programmed value is used. NTSEG1 is the sum of PROPAGATION TIME SEGMENT (PROP_SEG) and PHASE BUFFER SEGMENT1 (PHASE_SEG1). |
Bits 6:0 – NTSEG2[6:0] Time segment after sample point
| Value | Description |
|---|---|
| 0x00 - 0x7F | Valid values are 0 to 127. The actual interpretation by the hardware of this value is such that one more than the programmed value is used. NTSEG2 is PHASE BUFFER SEGMENT2 (PHASE_SEG2). |