Monroe Electronics Electrostatic Fieldmeter - Static Monitor - model 177A - Manual (Page 45)

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APPENDIX III
III.
RS-485 Half Duplex / Full (RS-422) Connection To 177A
RS-485 is a specialized interface that is very common in the data acquisition world . An RS-485 network can be
connected in a 2 or 4-wire mode (bi-directional - half duplex - multi-drop Communications over a single or dual
twisted pair cable). All the devices in the same network should be connected in daisy chain (see diagram below).
Maximum cable length can be as much as 4000 feet.
Tools and procedures to setup the 177A units for RS-485 communication:
 Station ID, RS-485 and Terminator setup.
 RS-232 to RS-485 Converter.
 Cable
Station ID, RS-485 and Terminator setup: Each 177A on the same RS-485 bus must have its own unique ID (1-
255). This can be set via ME177A software or from the front panel Setup. Baud rate is 9600 by default.
Setup RS-485 from the 177A front panel:
Press Key Display(blinking) Display Description
Setup Lo Front panel Lock
Up SS System Setup
Right bAu Baud rate
Down IT Interface Type
Right +232 RS-232
Down 485 - HAF RS-485 Half duplex
Enter
Setup Terminator (continue from above):
Press Key Display(blinking) Display Description
Left +485
Down TEr Terminator
Right on Press up/down to select terminator on / oFF
Enter
RS-485 Half Duplex
RS-232 or USB
to RS-485
Converter
Pin 2 3
177A
Unit 1
Termination enables
Termination enables
Up to 4000 feet
485 Data+
485 Data-
T+
R+
R-
T-
Pin 2 3
177A
Unit 2
Pin 2 3
177A
Unit n