In this section, the usage of the various bit-fields in the CANBTR register is illustrated.

The formula for bit-rate is:

Where BRP is the value of (BRP_reg + 1) and Bit-time = (TSEG1_reg + 1) + (TSEG2_reg + 1) + 1

In the above equations BRP_reg , TESG1_reg and TSEG2_reg represent the actual values written in the corresponding fields in the CANBTR register. The parameters TSEG1reg, TSEG2_reg, SJW_reg, and BRPreg are automatically enhanced by 1 when the CAN module accesses these parameters. If the BRPE field is used, it should be concatenated with the BRP field.

Example 1

Assume the following parameters are desired with a CAN module clock of 200 MHz:

Bit-rate = 500 kbps, SJW = 4, TSEG1 = 9 & TSEG2 = 6.

This is achieved by writing a value of 0x000058D8 in the CANBTR register. Here, TSEG1_reg = 8, TSEG2_reg = 5, SJW_reg = 3, and BRP_reg = 24

Effective BRP value = (BRP_reg + 1) = 25

Effective TSEG1 value = (TSEG1_reg + 1) = 9

Effective TSEG2 value = (TSEG2_reg + 1) = 6

Effective SJW value = (SJW_reg + 1) = 4

Bit-time = (TSEG1_reg + 1) + (TSEG2_reg + 1) + 1 = 16

Plugging these numbers into the bit-rate equation:

Example 2

Assume the following parameters are desired with a CAN module clock of 200 MHz:

Bit-rate = 50 kbps, SJW = 4, TSEG1 = 9 & TSEG2 = 6.

This is achieved by writing a value of 0x000358F9 in the CANBTR register. Here, TSEG1_reg = 8, TSEG2_reg = 5, SJW_reg = 3, BRPE = 11b , BRP = 111001b. Effective BRP_reg = 11111001b (249). Note that BRPE field is concatenated with the BRP field.

Effective BRP value = (BRP_reg + 1) = 250

Effective TSEG1 value = (TSEG1_reg + 1) = 9

Effective TSEG2 value = (TSEG2_reg + 1) = 6

Effective SJW value = (SJW_reg + 1) = 4

Bit-time = (TSEG1_reg + 1) + (TSEG2_reg + 1) + 1 = 16

Plugging these numbers into the bit-rate equation: