NXP Semiconductors MPC5606S - Baud Rate Generation

CAN Sampler
MPC5606S Microcontroller Reference Manual, Rev. 7
186 Freescale Semiconductor
7.4.3 Baud rate generation
Sampling is performed at a baud rate that is set by the software as a multiple of the RC oscillator frequency
of 62.5 ns (assuming RC is configured for high frequency mode of 16 MHz). The user must set the baud
rate prescaler (BRP) such that 8 samples per bit are achieved.
The baud rate must be set by software before going into Standby or Stop mode. This is done by setting
BRP bits 5:1 in the Control register. The reset value of BRP is 00000 and can be set to a maximum of
11111, which gives a prescale value of BRP + 1, thus providing a BRP range of 1 to 32.
• Maximum bit rate supported for sampling is 2 Mbit/s using BRP of 1
• Minimum bit rate supported for sampling is 62.5 kbit/s using BRP of 32
For example, suppose the system is transmitting at 125 kbit/s. In this case, the nominal bit period is:
T = 1/(125 × 10
3
)s = 8 × 10
–3
× 10
–3
s = 8 µs Eqn. 7-1
To achieve 8 samples per bit:
Sample period= 8/8 µs = 1 µs
BRP = 1 µs/62.5 ns = 16. Thus in this case, BRP = 01111.