16.7.1.1 CAN Bit-Timing Configuration
The CAN protocol specification partitions the nominal bit time into four different time segments:
SYNC_SEG:
This part of bit time is used to synchronize the various nodes on the bus. An edge is expected to lie
within this segment. This segment is always 1 TIME QUANTUM (TQ).
PROP_SEG:
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. This segment is programmable from 1 to 8 TIME QUANTA (TQ).
PHASE_SEG1:
This phase is used to compensate for positive edge phase error. This segment is programmable
from 1 to 8 TIME QUANTA (TQ) and can be lengthened by resynchronization.
PHASE_SEG2:
This phase is used to compensate for negative edge phase error. This segment is
programmable from 2 to 8 TIME QUANTA (TQ) and can be shortened by resynchronization.
In the eCAN module, the length of a bit on the CAN bus is determined by the parameters TSEG1 (BTC.6-3),
TSEG2 (BTC.2-0), and BRP (BTC.23.16).
TSEG1 combines the two time segments PROP_SEG and PHASE_SEG1 as defined by the CAN protocol.
TSEG2 defines the length of the time segment PHASE_SEG2.
IPT (information processing time) corresponds to the time necessary for the processing of the bit read. IPT
corresponds to two units of TQ.
The following bit timing rules must be fulfilled when determining the bit segment values:
• TSEG1(min) ≥ TSEG2
• IPT ≤ TSEG1 ≤ 16 TQ
• IPT ≤ TSEG2 ≤ 8 TQ
• IPT = 3/BRP (the resulting IPT has to be rounded up to the next integer value)
• 1 TQ ≤ SJW min[4 TQ, TSEG2] (SJW = Synchronization jump width)
• To utilize three-time sampling mode, BRP ≥ 5 has to be selected
Nominal bit time
SYNCSEG
1 TQ
TSEG2
TSEG1
Transmit point
Sample point
SJW
SJW
A.
TSEG1 can be lengthened or TSEG2 shortened by the SJW
Figure 16-6. CAN Bit Timing
Controller Area Network (CAN)
1012
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Содержание TMS320 2806 Series
Страница 2: ......