MC75172B Datasheet, PDF (10/12 Pages) ON Semiconductor – QUAD EIA-485 LINE DRIVERS

MC75172B MC75174B
Figure 18. Typical EIA–485 System
En
TTL
D
RT
#1
R
TTL
R
TTL TTL
#1
#2
5 “off” drivers (@ 0.06 U.L. each),
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+8 receivers (@ 1.0 U.L. each) = 8.3 Unit Loads
TTL
D
RT = 120 Ω at each end of the cable.
TTL
#2
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D
#3
R
#3
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TTL
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#4
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TTL
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RT
#6
TTL
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#8
R
TTL
#6
TTL
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#4
R
TTL
#7
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#5
TTL _TTL
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#5
120 Ω
Twisted
Pair
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.
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