AN1690

Fail-safe circuit comparisons with ST485EB

13/15

Figure 12.

Fail-safe DC termination - eye pattern and test circuit

Figure 13.

Fail-safe AC termination - eye pattern and test circuit

120

500

500

PRBS

GENERATOR

CH1

differential

probe

CH3

probe

100 Cable

130

Receiver

Input

Receiver

Output

120

500

500

PRBS

GENERATOR

CH1

differential

probe

CH3

probe

100 Cable

130

120

120

120

500

500

PRBS

GENERATOR

CH1

differential

probe

CH3

probe

100 Cable

130

Receiver

Input

Receiver

Output

Receiver

Input

Receiver

Output

C

Rc

Ra

Rb

C

Rb

PRBS

GENERATOR

CH1

differential

probe

CH3

probe

100m

cable

Receiver

Input

Receiver

Output

C

Rc

Ra

Rb

C

Rb

PRBS

GENERATOR

CH1

differential

probe

CH3

probe

100m

cable

C

Rc

Ra

Rb

Rb

C

Rb

C

Rb

Rb

PRBS

GENERATOR

CH1

differential

probe

CH3

probe

100m

cable

Receiver

Input

Receiver

Output

Receiver

Input

Receiver

Output