CAN FD System Design

International CAN Conference 2015, Vienna

Dr.–Ing. Marc Schreiner – Daimler AG

Overview:

• Acquisition and assessment of CAN FD signals

• Determination of a safe operation area for CAN FD topologies

• Typical characteristics of CAN FD topologies:

− Point to point link

− Line topology

− Bus topology with stubs

− Star topology

CAN FD System Design

Marc Schreiner, International CAN Conference 2015, Vienna2

Motivation

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0

0

200

400

600

800

1000

1200

1400

7575

78,575

75

76

80

80

757578,5

7575

7680

80

606057

56

60

60

60

60

6060

5756

60

60

60

60

phase m

arg

in (

ns)

Baudrate (Mbit/s)

PM1

PM2

sample point (%)

Marc Schreiner, International CAN Conference 2015, Vienna3

Bridge the gap between theory and application!

Theory: Definition of PM1 and PM2

Source: Robustness of a CAN FD Bus System – About Oscillator

Tolerance and Edge Deviations – A. Mutter, iCC 2013 Paris

Task: Design of a new CAN FD network

ECU1

T

ECU5

4m

2,5m

PC

7,5m

7m

0,3m

ECU4

2m

CAN

3m

ECU7ECU6

5m5m0,3m

T

ECU2 ECU3

TX

TX

TX

TX

TX

TX

TX

TX

RX

RX

RX

RX

RX

RX

RX

RX

µC

µC

µC

µC

CAN_H

CAN_H

CAN_H

CAN_H

CAN_L

CAN_L

CAN_L

CAN_L

CAN topologyunder test

CAN node 1 CAN node 1

CAN node n-1CAN node n

scope Tx1 (trigger)

scope bus 1 scope bus 2scope RX1 scope RX2

SE

SE

SE

SE

diff

diff

trigger once at all nodes

measure once at all nodesfor all trigger positions

result:matrix with n² measurements

Acquisition of CAN FD Signals within a Topology

Marc Schreiner, International CAN Conference 2015, Vienna4

Nod

e 1

Nod

e 2

Nod

e 3

Nod

e 4

Nod

e 5

Nod

e 6

Node 6

Node 5

Node 4

Node 3

Node 2

Node 1

receiver

tran

smit

ter

receiver

tran

smit

ter

Node

1

Node

2

Node

3

Node

4

Node

5

Node

6

Node 6

Node 5

Node 4

Node 3

Node 2

Node 1

0

1

2

3

4

71,50µ 71,75µ 72,00µ 72,25µ 72,50µ 72,75µ 73,00µ 73,25µ 73,50µ 73,75µ

-1

0

1

2

3

RX

/ T

X s

ign

al (V

)

logic transmitted TX

logic received RX

500mV

diffe

ren

tia

l b

us s

ign

al (V

)

differential bus signal at receiver

0.5V/0.9V transceiver thresholds

900mV

t(s)

Assessment of measured CAN FD Signals

Marc Schreiner, International CAN Conference 2015, Vienna5

RX

TX

CAN busringing!

virtual RX signal

based on bus signal

bit size based on

real RX signal

treatment of ringing not specified in ISO11898-2

ringing!

ringing!

Determine safe Operation Area for CAN FD Topologies

Marc Schreiner, International CAN Conference 2015, Vienna6

0

40n

80n

120n

160n

2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

asym

metr

ty (

s)

loopback signal

0 20 40 60 80 100 120

0

40n

80n

120n

160n

200ncommunication

between nodes

asym

metr

y (

s)

total bus length (m)

2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

0

40n

80n

120n

160n

2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

asym

metr

ty (

s)

loopback signal

0 20 40 60 80 100 120

0

40n

80n

120n

160n

200ncommunication between nodes

asym

metr

y (

s)

total bus length (m)

2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

evaluation based on real RX signal evaluation based on virtual RX signal

PM1, PM2 PM1, PM2

PM1, PM2 PM1, PM2

safety marginsafety margin

safety margin safety margin

safe topologies

safe topologies safe topologies

safe topologies

RX

TX

CAN bus

Node

1

Node

2

Node

3

Node

4

Node

5

Node

6

Node 6

Node 5

Node 4

Node 3

Node 2

Node 1

How to use the achieved Results

• The graphs given in the following show the typical characteristics of a set of

topologies with varying parameters at room temperature.

• The results include the topology and typical transceivers.

• The highlighted areas mark the range that contains all measured asymmetry

values of all variations that have been tested. These experimental results do

not claim to be exhaustive (e.g. temperature, tolerances etc.).

The highlighted areas are intended to be a

means of orientation and preselection.

The plots cannot replace a CAN FD system designer’s duty

to individually check a topology under development.

Marc Schreiner, International CAN Conference 2015, Vienna7

Point to Point Link

evaluation based on virtual RX signal

0

50n

100n

150n

200n

250n

300n

350n

both-sided term.

onesided term.

asym

metr

y (

s)

0 20 40 60 80 100 120

0

40n

80n

120n

160n

200n

both-sided term.

onesided term.

communication A→B

loopback signal

asym

metr

y (

s)

transmission line length (m)

communication stopped at

32m with test baudrate due to

high loop back asymmetry

0

50n

100n

150n

200n

250n

300n

350n

both-sided term.

onesided term.

asym

metr

y (

s)

0 20 40 60 80 100 120

0

40n

80n

120n

160n

200n

both-sided term.

onesided term.

communication A→B

loopback signal

asym

metr

y (

s)

transmission line length (m)

communication stopped at

32m with test baudrate due to

high loop back asymmetry

evaluation based on real RX signal

Marc Schreiner, International CAN Conference 2015, Vienna8

Line Topology with equally spaced Nodes

Marc Schreiner, International CAN Conference 2015, Vienna9

0

40n

80n

120n

160n 2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

12 nodes

14 nodes

asym

metr

ty (

s)

loopback signal

0 20 40 60 80 100 120

0

40n

80n

120n

160n

200ncommunication

between nodes

asym

metr

y (

s)

total bus length (m)

2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

12 nodes

14 nodes

0

40n

80n

120n

160n

asymmetry increasing

with number of nodes

2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

12 nodes

14 nodes

16 nodes

asym

metr

ty (

s)

loopback signal

0 20 40 60 80 100 120

0

40n

80n

120n

160n

200n

asymmetry increasing

with bus length

communication between nodes

asym

metr

y (

s)

total bus length (m)

2 nodes

3 nodes

4 nodes

5 nodes

6 nodes

7 nodes

8 nodes

12 nodes

14 nodes

16 nodes

asymmetry increasing

with number of nodes

evaluation based on real RX signal evaluation based on virtual RX signal

Bus Topology with Stubs of equal Length

0

100n

200n

300n

400n

500n

600n

ls ≤ 0,25m

ls ≤ 0,5m

ls ≤ 1m

ls ≤ 2m

ls ≤ 2m

ls ≤ 1m

ls ≤ 0,5m

ls ≤ 0,25m

loopback signal 1 stub

2 stubs

3 stubs

4 stubs

5 stubs

6 stubs

asym

metr

ty (

s)

0 20 40 60

0

100n

200n

300n

400n

500n

600n communication between nodes

asym

metr

y (

s)

main bus length (m)

1 stub

2 stubs

3 stubs

4 stubs

5 stubs

6 stubs

0

100n

200n

300n

400n

500n

600n

��

�� ls = 0,25 m

� ls = 0,5 m

� ls = 1 m

� ls = 2 m

� ls = 4 m

�

asymmetry increasing with

number of stubs and stub length

1 stub

2 stubs

3 stubs

4 stubs

5 stubs

6 stubs

asym

metr

ty (

s)

loopback signal

�

0 20 40 60

0

100n

200n

300n

400n

500n

600n

asym

metr

y (

s)

main bus length (m)

1 stub

2 stubs

3 stubs

4 stubs

5 stubs

6 stubs

communication between nodes

�� �

� �

� ls = 0,25 m

� ls = 0,5 m

� ls = 1 m

� ls = 2 m

� ls = 4 m

asymmetry increasing with

number of stubs and stub length

evaluation based on real RX signal evaluation based on virtual RX signal

Marc Schreiner, International CAN Conference 2015, Vienna10

Bus Topology with Stubs and one offset Stub

0

100n

200n

300n

400n

500n

600n

700n offset stub length

� lo = 1,25 m

� lo = 1,5 m

� lo = 2 m

� lo = 3 m

� lo = 5 m

1 sub / 1 offset stub

2 subs / 1 offset stub

3 subs / 1 offset stubls = const. = 1m

loopback signal

asym

metr

ty (

s)

�

�

�

�

�

�

�

�

�

�

0 20 40

0

100n

200n

300n

400n

500n

600n

700n

offset stub length

� lo = 1,25 m

� lo = 1,5 m

� lo = 2 m

� lo = 3 m

� lo = 5 m

ls = const. = 1m

asym

metr

y (

s)

main bus length (m)

1 sub / 1 offset stub

2 subs / 1 offset stub

3 subs / 1 offset stub

communication between nodes0

100n

200n

300n

400n

500n

600n

700n loopback signal 1 sub / 1 offset stub

2 subs / 1 offset stub

3 subs / 1 offset stub

��

�

asym

metr

ty (

s)

offset stub length

� lo = 1,25 m

� lo = 1,5 m

� lo = 2 m

� lo = 3 m

� lo = 5 m

�

�

��

�

�

�

��

�

�

�

other stubs:

ls = const. = 1m

0 20 40

0

100n

200n

300n

400n

500n

600n

700n

offset stub length

� lo = 1,25 m

� lo = 1,5 m

� lo = 2 m

� lo = 3 m

� lo = 5 m

other stubs:

ls = const. = 1m

communication between nodes

asym

metr

y (

s)

main bus length (m)

1 sub / 1 offset stub

2 subs / 1 offset stub

3 subs / 1 offset stub

evaluation based on real RX signal evaluation based on virtual RX signal

Marc Schreiner, International CAN Conference 2015, Vienna11

Star Topology with Ferrites inside the Star

0

100n

200n

300n

400n

500n

600n

3 branches

4 branches

5 branches

6 branches

7 branches

8 branches

12 branches

asym

metr

ty (

s)

loopback signal

not analysable,

ringing > tBit

not analysable,

ringing > tBit

0 2 4 6 8

0

100n

200n

300n

400n

500n

communication between nodes

asym

metr

y (

s)

branch length (m)

3 branches

4 branches

5 branches

6 branches

7 branches

8 branches

12 branches

0

100n

200n

300n

400n

500n

600n

low loopback asymmetry

3 branches

4 branches

5 branches

6 branches

7 branches

8 branches

12 branchesasym

metr

ty (

s)

loopback signal

asymmetry increasing

with number of branches

0 2 4 6 8

0

100n

200n

300n

400n

500n

communication between nodes

asym

metr

y (

s)

branch length (m)

3 branches

4 branches

5 branches

6 branches

7 branches

8 branches

12 branches

evaluation based on real RX signal evaluation based on virtual RX signal

Marc Schreiner, International CAN Conference 2015, Vienna12

CAN FD System Design – Conclusion

A workflow for the assessment of CANFD topologies has been presented.

The maximum asymmetry of various CAN FD topologies has been compared,

based on the logic RX signal and on the signal quality on the bus lines.

Point to point link and line topology:

• most suitable for high communication speeds, very low ringing

• lowest risks for signal integrity issues

Bus topology with stubs:

• trade-offs have to be made for higher communication speeds

• ringing on the bus lines causes risks for signal integrity issues

• if stubs are needed they should be as short as possible

Star topology (star including ferrites):

• only suitable for high communication speed if branches are very short

Marc Schreiner, International CAN Conference 2015, Vienna13

CAN FD System Design

International CAN Conference 2015, Vienna

Dr.–Ing. Marc Schreiner – Daimler AG

Backup

• Exemplary signal shapes

• Safety margin

Marc Schreiner, International CAN Conference 2015, Vienna15

Exemplary Signal Shapes

Marc Schreiner, International CAN Conference 2015, Vienna16

0

1

2

3

4

5

79,0µ 79,5µ 80,0µ 80,5µ 81,0µ

-1

0

1

2

3

504

n

507,2

n

507,2

n

492,8

n

492,8

n

BY

TE

6 B

IT5

BY

TE

6 B

IT4

BY

TE

6 B

IT3

BY

TE

6 B

IT2

BY

TE

6 B

IT1

RX

/TX

(V

)

TX ID: 201

RX

Bit Length Dom FD

Bit Length Rez FD

Sample Points

diff.

Bus (

V)

t (s)

0.9V / 0.5V

Bus TX

Bus RX

0

1

2

3

4

5

79,0µ 79,5µ 80,0µ 80,5µ 81,0µ

-1

0

1

2

3

531,2

n

532,8

n

534,4

n

467,2

n

467,2

n

BY

TE

6 B

IT5

BY

TE

6 B

IT4

BY

TE

6 B

IT3

BY

TE

6 B

IT2

RX

/TX

(V

)

TX ID: 200

RX

Bit Length Dom FD

Bit Length Rez FD

Sample Points

diff.

Bus (

V)

t (s)

0.9V / 0.5V

Bus TX

Bus RX

point to point link with

single sided termination

point to point link with

termination at both sides

Exemplary Signal Shapes

Marc Schreiner, International CAN Conference 2015, Vienna17

0

1

2

3

4

5

74,0µ 74,5µ 75,0µ

-1

0

1

2

3

540,8

n

459,2

n

459,2

n

BY

TE

6 B

IT2

BY

TE

6 B

IT1

BY

TE

6 B

IT0

RX

/TX

(V

)

TX ID: 206

RX

Bit Length Dom FD

Bit Length Rez FD

Sample Points

diff.

Bus (

V)

t (s)

0.9V / 0.5V

Bus TX

Bus RX

bus with stubs

(measured at long stub line)

line topology

(measured at mid-node)

0

1

2

3

4

5

73,0µ 73,5µ 74,0µ 74,5µ 75,0µ

-1

0

1

2

3

504n

502,4

n

496n

49

7,6

n

496n

BY

TE

6 B

IT4

BY

TE

6 B

IT3

BY

TE

6 B

IT2

BY

TE

6 B

IT1

BY

TE

6 B

IT0

RX

/TX

(V

)

TX ID: 202

RX

Bit Length Dom FD

Bit Length Rez FD

Sample Points

diff.

Bus (

V)

t (s)

0.9V / 0.5V

Bus TX

Bus RX

Exemplary Signal Shapes

Marc Schreiner, International CAN Conference 2015, Vienna18

0

1

2

3

4

5

73,0µ 73,5µ 74,0µ 74,5µ 75,0µ

-1

0

1

2

3

643,2

n

643,2

n

355,2

n

356,8

n

356,8

n

BY

TE

6 B

IT4

BY

TE

6 B

IT3

BY

TE

6 B

IT2

BY

TE

6 B

IT1

BY

TE

6 B

IT0

RX

/TX

(V

)

TX ID: 206

RX

Bit Length Dom FD

Bit Length Rez FD

Sample Points

diff.

Bus (

V)

t (s)

0.9V / 0.5V

Bus TX

Bus RX

star topology

(measured at long branch)

CANFD Safety Margin

CAN FD from a view point of an OEM, Marc Schreiner - Daimler AG, 12. Nov. 2013, iCC 2013 Paris19

topology delay and symmetryworst case transceiver

characteristicsclock

tolerancesjitter

EMIjitter

margin for future

extensions

+ PLL

temperatureeffects other circuitry effects

aging

ISO11898-2