11.12 Rules for Correct Setting of Baud Rate
The CAN protocol limit values for ensuring correct operation of FCAN are described below. If these limit values are
exceeded, a CAN protocol violation may occur, which can result in operation faults. Always make sure that settings
are within the range of limit values.
(a) 5 × BTL ≤ SPT (sampling point) ≤ 17 × BTL [4 ≤ SPT4 to SPT0 set values ≤ 16]
(b) 8 × BTL ≤ DBT (data bit time) ≤ 25 × BTL [7 ≤ DBT4 to DBT0 set values ≤ 24]
(c) SJW (synchronization jump width) ≤ DBT − SPT
(d) 2 × (DBT − SPT) ≤ 8
Remark
BTL = 1/f
BTL
SPT4 to SPT0 (Bits 9 to 5 of CAN1 synchronization control register (C1SYNC))
DBT4 to DBT0 (Bits 4 to 0 of CAN1 synchronization control register (C1SYNC))
(1) Example of FCAN baud rate setting (when C1BRP register's TLM bit = 0)
The following is an example of how correct settings for the C1BRP register and C1SYNC register can be
calculated.
Conditions from CAN bus:
<1> CAN base clock frequency (f
<2> CAN bus baud rate: 83 kbps
<3> Sampling point: 80% or more
<4> Synchronization jump width: 3 BTL
First, calculate the ratio between the CAN base clock frequency and the CAN bus baud rate frequency as
shown below.
/CAN bus baud rate = 16 MHz/83 kHz ≠ 192.77 ≠ 2
f
MEM
Set an even number between 2 and 128 to the C1BRP register's bits BRP5 to BRP0 as the setting for the
prescaler (CAN protocol layer base system clock: f
register's bits DBT4 to DBT0 as the data bit time.
Since it is assumed that the SJW (synchronization jump width) value is 3, the maximum setting for SPT
(sampling point) is 3 less than the data bit time setting and is 17.
(SPT ≤ DBT – 3 and SPT = 17)
CHAPTER 11 FCAN CONTROLLER
(f
: CAN protocol layer base system clock)
BTL
): 16 MHz
MEM
User's Manual U14492EJ5V0UD
× 3
6
), then set a value between 8 and 25 to the C1SYNC
BTL
615