modbus+ and sa85 card under win98


Thread Starter


I want to read data from modicon plc through modbus+ protocol and sa85 card,but sa85 card does not work normally under win98,i haven't sa85 card driver,i know modbus+ is a RS-485 protocol, can I use RS-232 to RS-485 convert product to read data from plc, and who tell me modbus+ protocol? is there any way reading data?
You can't just use a RS232/485 converter because Modbus serial is a master/slave protocol and Modbus+ is a token ring protocol.

Check into using a Bridge Multiplexer (BM85-series) from Modicon which has a Modbus+ port and 4 Modbus serial ports. Each serial port can be individually configured for ASCII/RTU, baud rate, etc. We've used them a lot where we put a modem on the serial port, it lets us remote dial into a Modbus+ network.

Don Zunti
Delco Automation Canada
You have to use a modbus plus adaptor of some sort. There is a driver that will work under win98 any 32bit version that contains the lnet libary and virtual device driver should work ok. Yes it is a rs-485 network. But it is a constant carrier signal using phase shift to encode the data and its token ring so you can't use a 232 to 485 convertor, only a modbus to moblus plus bridge multiplexer (bm-85) can patch rs-232 modbus commands onto the modbus plus network. The easiest way with out a sa-85 or bm-85 is to talk rs-232 modbus directly into a spare modbus port on a Modicon PLC that has been cofigured to be in bridge mode. This will give you access to the MB+ network connected to the PLC.
Where did you hear that Modbus-Plus is an RS-485 protocol ? RS-485 is not a protocol nor does it generally run at 1 Mbaud or know how to pass Modbus-Plus tokens around.

Modicon sells a set of Modbus-Plus drivers that work just fine on Win95 with an SA85 card. Did you install these drivers and run the MBPSTAT utility to check your network ?

Jay Kirsch
Easiest and most effective solution will be to buy the driver suite. It's part number is SWMXDS001 and any Modicon distributor can get it for you. As for how to read Modbus Plus, it's a proprietary network, the spec is not open. You would have to buy a license to it from Modicon (and I'm sure that's alot more expensive than the driver suite for the SA85 you said you already have.)
Thread starter Similar threads Forum Replies Date
C Modbus 2
A Modbus 2
M Modbus 2
T Modbus 11
M Modbus 5