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General => Technical support => Topic started by: Allan on June 13, 2002, 10:36:30 AM

Title: Modbus-RTU device connection
Post by: Allan on June 13, 2002, 10:36:30 AM

Hi

We have wired the RS-232 Host Link/Modbus Port on the T100MD888+ to PC as normal and are attempting to connect a 3rd party Modbus device to the RS-485 port.  The Modbus-RTU device supplier recommends the following RS-485 connection to the PLC:

(http://C:\My Documents\AA files\Work\projects\MSc\Nuri Tlag\Image1.jpg)

The PLC RS-485 port only has a +ve and -ve terminal - there is no GRN terminal?  How do we achieve the above wiring to the host PLC?  Any suggestions gratefully received

Allan & Nuri :'(

Title: Re: Modbus-RTU device connection
Post by: david reed on June 15, 2002, 08:51:21 AM

Allan,
 
Data+ to +ve
Data- to -ve
 
Do not leave the DEFAULT* jumper connected to ground. This should only be jumpered to ground during "configuration" of the module. Modbus protocol will not work while the DEFAULT* line is connected to ground.
 
Please make sure that the power supply to the module is connected to EARTH GROUND and so is the ground of the PLC.
 
Regards,
David Reed
DGH Corporation, USA