M16C Datasheet, PDF (167/262 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Preliminary Specifications REV.B
Mitsubishi microcomputers
Specifications in this manual are tentative and subject to change.
M16C / 6N Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
CAN Module
CAN Configuration Register
A programmable clock prescaler is used to derive the CAN module basic clock from the clock frequency
f(CAN0/1)/2. Bit 0 to bit 3 of the CAN configuration register represent the prescaler, allowing a division ratio
of 1 to 1/16 to be selected. So the CAN module basic clock frequency fCANB can be calculated as follows:
f(CAN0/1)
f_CANB
=
-----------------------------------------
2 x (BRP + 1)
where BRP is the value of the prescaler (selectable from 0 to 15). The effective baud rate of the CAN bus
communication depends on the CAN bus timing control parameters and will be explained below.
fCAN0
1/2
1/BRP0
fCAN1
1/2
1/BRP1
Figure 18-4. Generation of CAN basic clock frequency
CAN bus timing control
Each bit-time consists of four different segments:
fCANB0
fCANB1
Bit-time
SS
PR
PH1
PH2
Sample point
Synchronization segment (SS),
Propagation time segment (PR),
Phase buffer segment 1 (PH1) and
Phase buffer segment 2 (PH2).
Figure 18-5. Bit timing
The first segment (SS) is fixed to one Time Quantum, the segments PR, PH1 and PH2 can be programmed
from 1 to 8 Time Quanta by the CAN configuration register. The whole bit-time has to consist of minimum 8
and maximum 25 Time Quanta. The duration of one Time Quantum is the cycle time of fCANB.
f(CAN0/1)
Baudrate
=
-------------------------------------------------------------------------
2 x (BRP + 1) x Num(quanta)
For example: assuming f(X_IN)=16MHz and BRP=0, one Time Quantum will be 125ns long. This allows a
maximum transmission rate of 1Mbps (assuming 8 Time Quanta per bit-time).
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