Control logix RS232 port

[Guest]

I want to use a 1756 processor RS232 port and link for bi directional communications with a RS485 link to one device. Can anybody suggest a good 232---485 converter? I know line powered converter are troublesome. Also, are there any software traps I should be aware of?

Thanks in advance

 

[jvdcande]

Why not use the converter from AB itself? Order number is 1761-NET-AIC.

Kind regards,

 

[Ken Roach]

Remember that if you use a "two-wire" RS-485 converter (like the 1761-Net-AIC) you won't be able to run DF1 Full Duplex because "two-wire" RS-485 doesn't allow simultaneous transmission and reception.

What protocol do you need to run over this RS-485 interface ?

 

[Guest]

Protocol

Ken
The instrument communicates digitally via RS485 half duplex. There is one device communicating on this serial link. The Control Logix sends setpoints, the instrument returns a stream of values......the controller resends setpoint info....the instrument returns with yet another stream of measured values. The bit stream is coming about every 3mS

Hardware wise...which Rs-232 to RS-485 converter is suggested

Software wise......Can the Control Logix controller handle this fast of a data stream? Are there any software tricks that make processing this data more effciently?

Thanks in advance

Happy Thanksgiving!

 

[Ken Roach]

Is this strictly an ASCII command/response protocol, or is it something like Modbus ?

If the device requires a string from the controller in order to send it's reply string, then you shouldn't have a problem with Logix correctly receiving and interpreting the string.

You said the "bit stream is coming every 3 ms", which is confusing to me. Usually you express serial data speed as a "baud rate", most commonly 9600 baud to 38,400 baud.

Can you tell us about the device ? It's probably RS-485 two-wire, but just knowing that it is half-duplex doesn't conclusively tell us how to hook it up. The 1761-Net-AIC is a good isolating RS-232/485 converter with an isolated common wire as well as the Signal A and Signal B wires.