MC75172B MC75174B

10

MOTOROLA ANALOG IC DEVICE DATA

Figure 18. Typical EIA–485 System

NOTES: 1. Terminating resistors RT must be located at the physical ends of the cable.

2. Stubs should be as short as possible.

3. Circuit ground of all drivers and receivers must be connected via a dedicated wire within the cable.

Do not rely on chassis ground or power line ground.

#8

TTL

R

TTL

TTL

#3

TTL

R

En

#2

TTL

TTL

En

TTL

R

TTL

#1

R

TTL

RT

#1

En

D

#3

D

#5

D

TTL

En

#6

R

TTL

R

En

#5

R

#6

D

#7

RT

TTL

TTL

R

En

TTL

#4

D

5 “off” drivers (@ 0.06 U.L. each),

+8 receivers (@ 1.0 U.L. each) = 8.3 Unit Loads

RT = 120 Ω at each end of the cable.

#4

D

#2

120

Ω

Twisted

Pair