EasyGrid LT User Guide
28
RS-422/485
5.5
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Please refer to the Communication Configuration section for dip switch settings
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The EasyGrid LT RS-422/485 communication port is half duplex.
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FISO recommends the use of a two shielded twisted pair cable for RS-485 mode and a three
shielded twisted pair cable for RS-422. The extra pair will be used for ground.
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If the EasyGrid LT is at one end of the cable you must place an End Of Line resistor. You can use
the integrated EOL resistance with the Off/RS485 EOL R dip switch.
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FISO recommends polarising the link in one place. You could use the integrated pull up and pull
down resistors of the EasyGrid LT. To do so, place the Off/RS485 Pull Up and the Off/RS485 Pull
Down dip switch to the right.
A and B Circuit Designators
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The ‘A’ and ‘B’ circuit designators are often a source of confusion.
To determine which terminal is ‘A’ and which is ‘B’, set the line to the ‘Idle’ or ‘Off’ state. Connect a
multi-meter on the volts range across the ‘A’ and ‘B’ terminals. When the multi-meter reads a positive
voltage, the positive terminal of the multi-meter is connected to ‘B’ and GND terminal is connected to
‘A’.
This is why we write ‘B+’ and ‘A-’ on the EasyGrid LT.
It is important to refer to the manufacturer’s handbook or to test the line as in the previous paragraph.
