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UMRR-0Axxxx Type31 Operational Description.docx Version 1
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Page 12
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August 22, 2013
7
Data interfaces
7.1
CAN data interface
This specification gives a detailed description of the CAN data communication used in the
UMRR based systems on the sensor CAN. The UMRR is compliant with CAN 2.0B standard.
CAN is a very robust full duplex bidirectional interface.
7.2
CAN-Settings
Baud Rate:
500kBit/s or lower
T
seg1
:
8
T
seg2
:
7
T
sjw
:
1
(SJW: synchronization jump width)
Above values for CAN bit timing are illustrated in Figure 7 for the DSP TI TMS320F28335
used in the UMRR radar sensor (note: the eCAN module is integrated in the DSP). For
comparison purposes, in Figure 8 the CAN bit timing as defined by the CAN protocol is
shown. For the DSP TMS320F28335 the value of SYNCSEG (Figure 7) is always equal to 1 TQ
(Time Quantum) and it corresponds to the value Sync in Figure 8. TSEG1 (Figure 7)
combines the two time segments Prop and Phase 1 (Figure 8) as defined by the CAN
protocol. TSEG2 (Figure 7) corresponds to Phase 2 (Figure 8)
The CAN bit timing parts as defined by the CAN protocol (Figure 8) can be described as
follows:
Sync
: This part of bit time is used to synchronize the various nodes on the bus. An
edge is expected to lie within this segment. For the UMRR sensor, this segment is
always 1 TIME QUANTUM (TQ).
Prop
: This part of the bit time is used to compensate for the physical delay times
within the network. It is twice the sum of the signal’s propagation time on the bus
line, the input comparator delay, and the output driver delay. For the UMRR sensor,
this segment is programmable from 1 to 8 TIME QUANTA (TQ.
Phase 1
: This phase is used to compensate for positive edge phase error. For the
UMRR sensor, this segment is programmable from 1 to 8 TIME QUANTA (TQ) and
can be lengthened by resynchronization.
Phase 2
: This phase is used to compensate for negative edge phase error. For the
UMRR sensor, this segment is programmable from 2 to 8 TIME QUANTA (TQ) and
can be shortened by resynchronization.
