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Bit-Timing Configuration Register (CANBTC)
Bit
Field
Value
Description
7
SAM
This parameter sets the number of samples used by the CAN module to determine the actual level
of the CAN bus. When the SAM bit is set, the level determined by the CAN bus corresponds to the
result from the majority decision of the last three values. The sample points are at the sample point
and twice before with a distance of TQ.
1 The CAN module samples three times and make a majority decision. The triple sample mode
shall be selected only for bit rate prescale values greater than 4 (BRP > 4).
0 The CAN module samples only once at the sampling point.
6:3
TSEG1 3:0
Time segment 1. The length of a bit on the CAN bus is determined by the parameters TSEG1,
TSEG2, and BRP. All controllers on the CAN bus must have the same baud rate and bit length. For
different clock frequencies of the individual controllers, the baud rate has to be adjusted by the said
parameters.
This parameter specifies the length of the TSEG1 segment in TQ units. TSEG1 combines
PROP_SEG and PHASE_SEG1 segments:
TSEG1 = PR PHASE_SEG1
where PROP_SEG and PHASE_SEG1 are the length of these two segments in TQ units.
TSEG1reg denotes the "register value" of "time segment 1;" i.e., the value written into bits 6:3 of the
CANBTC register. This value is automatically enhanced by 1 when the CAN module accesses it.
This enhanced value is denoted by the symbol TSEG1.
TSEG1 = TSEG1
reg
+ 1
TSEG1 value should be chosen such that TSEG1 is greater than or equal to TSEG2 and IPT. For
more information on IPT, see Section 3.1.1.
2:0
TSEG2
reg
Time Segment 2. TSEG2 defines the length of PHASE_SEG2 segment in TQ units:
TSEG2 is programmable in the range of 1 TQ to 8 TQ and has to fulfill the following timing rule:
TSEG2 must be smaller than or equal to TSEG1 and must be greater than or equal to IPT.
TSEG2reg denotes the "register value" of "time segment 2;" i.e., the value written into bits 2:0 of the
CANBTC register. This value is automatically enhanced by 1 when the CAN module accesses it.
This enhanced value is denoted by the symbol TSEG2.
TSEG2 = TSEG2
reg
+ 1
SPRU074F – May 2002 – Revised January 2009
eCAN Registers
41