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M16C/6N Group (M16C/6NK, M16C/6NM)
19.6 Configuration CAN Module System Clock
The M16C/6N Group (M16C/6NK, M16C/6NM) has a CAN module system clock select circuit.
Configuration of the CAN module system clock can be done through manipulating the CCLKR register and
the BRP bit in the CiCONR register (i = 0, 1).
For the CCLKR register, refer to 8. Clock Generating Circuit.
Figure 19.14 shows a block diagram of the clock generating circuit of the CAN module system.
f1
fCAN
P
fCANCLK : CAN communication clock fCANCLK = fCAN/2(P + 1)
Figure 19.14 Block Diagram of CAN Module System Clock Generating Circuit
19.7 Bit Timing Configuration
The bit time consists of the following four segments:
• Synchronization segment (SS)
This serves for monitoring a falling edge for synchronization.
• Propagation time segment (PTS)
This segment absorbs physical delay on the CAN network which amounts to double the total sum of
delay on the CAN bus, the input comparator delay, and the output driver delay.
• Phase buffer segment 1 (PBS1)
This serves for compensating the phase error. When the falling edge of the bit falls later than expected,
the segment can become longer by the maximum of the value defined in SJW.
• Phase buffer segment 2 (PBS2)
This segment has the same function as the phase buffer segment 1. When the falling edge of the bit
falls earlier than expected, the segment can become shorter by the maximum of the value defined in SJW.
Figure 19.15 shows the bit timing.
The range of each segment: Bit time = 8 to 25Tq
Figure 19.15 Bit Timing
Rev.2.00
Nov 28, 2005
REJ09B0124-0200
Divide-by-1 (undivided)
CAN module
Divide-by-2
system clock
Divide-by-4
divider
Divide-by-8
Divide-by-16
Value: 1, 2, 4, 8, 16
CCLKR register
: CAN module system clock
: The value written in the BRP bit in the CiCONR register ( i = 0, 1). P = 0 to 15
Bit time
SS
PTS
SS = 1Tq
PTS = 1Tq to 8Tq
PBS1 = 2Tq to 8Tq
PBS2 = 2Tq to 8Tq
SJW = 1Tq to 4Tq
page 237 of 378
Prescaler
fCAN
Baud rate
1/2
prescaler
division value
: P + 1
CAN module
PBS1
PBS2
SJW
SJW
Sampling point
Configuration of PBS1 and PBS2: PBS1 ≥ PBS2
19. CAN Module
fCANCLK
PBS1 ≥ SJW
PBS2 ≥ 2 when SJW = 1
PBS2 ≥ SJW when 2 ≤ SJW ≤ 4
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