Motorola MVME2603-1121A, 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-1 and Table C-4 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-6. 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