CAN Operation
9-10
ADSP-BF537 Blackfin Processor Hardware Reference
CAN_CLOCK
register. Although the
BRP
field can be set to any value, it is rec-
ommended that the value be greater than or equal to 4, as restrictions
apply to the bit timing configuration when
BRP
is less than 4.
The
CAN_CLOCK
register defines the TQ value, and multiple time quanta
make up the duration of a CAN bit on the bus. The
CAN_TIMING
register
controls the nominal bit time and the sample point of the individual bits
in the CAN protocol.
shows the three phases of a CAN bit—
the synchronization segment, the segment before the sample point, and
the segment after the sample point.
The synchronization segment is fixed to one TQ. It is required to syn-
chronize the nodes on the bus. All signal edges are expected to occur
within this segment.
The
TSEG1
and
TSEG2
fields of
CAN_TIMING
control how many TQs the
CAN bits consist of, resulting in the CAN bit rate. The nominal bit time
is given by the formula
tBIT
=
TQ
x (
1
+ (
1
+
TSEG1
) + (
1
+
TSEG2
)). For safe
receive operation on given physical networks, the sample point is pro-
grammable by the
TSEG1
field. The
TSEG2
field holds the number of TQs
needed to complete the bit time. Often, best sample reliability is achieved
with sample points in the high 80% range of the bit time. Never use sam-
ple points lower than 50%. Thus,
TSEG1
should always be greater than or
equal to
TSEG2
.
Figure 9-7. Three Phases of a CAN Bit
TQ
TQ
NOMINAL BIT TIME
TQ x (TSEG2 + 1)
TQ
TQ
TQ
TQ
TQ
TQ
TQ
TQ
t
TQ
TQ
TQ
SYNC
TQ x (TSEG1 + 1)
SAMPLE POINT
TRANSMIT POINT
TQ
TQ
Summary of Contents for Blackfin ADSP-BF537
Page 42: ...Contents xlii ADSP BF537 Blackfin Processor Hardware Reference ...
Page 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 138: ...Programming Examples 4 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 606: ...Programming Examples 9 94 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 660: ...Programming Examples 10 54 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 840: ...Programming Examples 13 42 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 876: ...Programming Examples 14 36 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 938: ...Programming Examples 15 62 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 958: ...Programming Examples 17 12 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 986: ...Programming Examples 18 28 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Page 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...