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Voltage References

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TTL<br />

5 "off" drivers (@0.06 U.L each),<br />

+8 receivers (@ 1.0 U.L each) = 8.3 Unit Loads<br />

RT = 120 Q at each end of the cable.<br />

MC75172B, MC75174B<br />

Figure 18. Typical EIA-485 System<br />

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NOTES:<br />

1) Terminating resistors RT must be located at the physical ends of the cable.<br />

2) Stubs should be as short as possible.<br />

3) Circuit ground of all drivers and receivers must be connected via a dedicated wire within the cable.<br />

Do not rely on chassis ground or power line ground.<br />

TTL<br />

TTL<br />

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MOTOROLA LINEAR/INTERFACE ICs DEVICE DATA<br />

7-191<br />

120Q<br />

Twisted<br />

Pair

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