Motorola MVME1603, Инструкция по установке и эксплуатации

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Serial Interconnections
C-9
C
Proper Grounding
An important subject to consider is the use of ground pins. There are two
pins labeled GND. Pin 7 is the signal ground and must be connected to the
distant device to complete the circuit. Pin 1 is the chassis ground, but it
must be used with care. The chassis is connected to the power ground
through the green wire in the power cord and must be connected to be in
compliance with the electrical code.
The problem is that when units are connected to different electrical outlets,
there may be several volts of difference in ground potential. If pin 1 of each
device is interconnected with the others via cable, several amperes of
current could result. This condition may not only be dangerous for the
small wires in a typical cable, but may also produce electrical noise that
causes errors in data transmission. That is why Table C-2 and Table C-5
show no connection for pin 1. Normally, pin 7 (signal ground) should only
be connected to the chassis ground at one point; if several terminals are
used with one computer, the logical place for that point is at the computer.
The terminals should not have a connection between the logic ground
return and the chassis.
Table C-7. EIA-530 Interface Receiver Characteristics
Parameter
Value
Unit
Minimum Maximum
Differential input voltage
±
12 V
Input offset voltage
±
12 V
Differential input high threshold voltage 200 mV
Differential input low threshold voltage
−
200 V
Input hysteresis 1.0 V
Input impedance (
−
15V < V
in
< +15V) 3000 7000
Ω